applied sciences

Article Component Materials, 3D Digital Restoration, and Documentation of the Imperial Gates from the Wooden Church of Voivodeni, Sălaj County,

1, 2 3 3 3 Călin Neamt, u * , Ioan Bratu , Constantin Mărut, oiu , Victor Constantin Mărut, oiu , Olivia Florena Nemes, , 1 1, 1 1 Radu Comes ,S, tefan Bodi * , Zsolt Buna and Daniela Popescu

1 Department of Design Engineering and Robotics, Faculty of Machine Building, Technical University of Cluj-Napoca, 103-105 Muncii Blvd., 400641 Cluj-Napoca, Romania; [email protected] (R.C.); [email protected] (Z.B.); [email protected] (D.P.) 2 National Institute for R&D of Isotopic and Molecular Technologies, 67-103 Donat St., 400293 Cluj-Napoca, Romania; [email protected] 3 Faculty of Orthodox Theology, “Babes, -Bolyai” University, F/N Episcop Nicolae Ivan St., 400117 Cluj-Napoca, Romania; [email protected] (C.M.); [email protected] (V.C.M.); [email protected] (O.F.N.)

* Correspondence: [email protected] (C.N.); [email protected] (S, .B.)

Abstract: The wooden churches from , Romania, are a unique and representative cultural   heritage asset for rural communities, both in terms of architecture and the style of painting that defines them as monuments of national heritage. These churches are in danger of degradation Citation: Neamtu, C.; Bratu, I.; , because rural communities are beginning to abandon them for various motives (e.g., they are too M˘arutoiu, C.; M˘arutoiu, V.C.; Nemes, , , , small, are expensive to maintain, or are being replaced by modern churches, built of stone and modern O.F.; Comes, R.; Bodi, S, .; Buna, Z.; materials). The reason behind their accelerated degradation is that they are covered with shingles Popescu, D. Component Materials, 3D Digital Restoration, and that need to be periodically changed and repaired to prevent water from reaching the inner painting Documentation of the Imperial Gates layer, a process that is, in many cases, ignored. Imperial gates are the symbol of these churches and from the Wooden Church of separate the nave from the narthex. They are made entirely out of wood and were sculpted and Voivodeni, Sălaj County, Romania. painted manually by skilled craftsmen and still represent the central element of these churches, in Appl. Sci. 2021, 11, 3422. terms of art and aesthetics. The digital preservation of these heritage assets is an interdisciplinary https://doi.org/10.3390/ undertaking, which begins with the physico-chemical analysis of the pigments in the painting layer, app11083422 continues with three-dimensional (3D) of the monument and of the objects of interest (such as the imperial gates), and finishes with a digital restoration of these monuments and artefacts. Academic Editor: Marek Milosz This paper presents a working methodology, successfully applied in digitizing and digitally restoring imperial gates from wooden churches in Transylvania, namely from the wooden church of Voivodeni, Received: 15 March 2021 Sălaj County, Romania (Transylvania region). X-ray fluorescence and FTIR were used Accepted: 8 April 2021 to determine the pigments in the painting layer of these artefacts, and after they were identified, they Published: 11 April 2021 were synthesized in laboratory conditions. The resulting color was digitized and used for digitally

Publisher’s Note: MDPI stays neutral restoring the artefact(s) to its (their) pristine condition. To popularize these cultural heritage assets, with regard to jurisdictional claims in the authors make use of to mediate the interaction between the general public and published maps and institutional affil- heritage objects in their current state of preservation, in a digital environment. Moreover, to showcase iations. how these heritage objects were degraded over time, a digitally restored version of the artefact in pristine condition is presented alongside a version in its current state (as is, digitized, but not yet digitally restored).

Copyright: © 2021 by the authors. Keywords: Fourier-transform IR spectroscopy; X-ray fluorescence spectroscopy; digital restoration Licensee MDPI, Basel, Switzerland. of cultural heritage; digital preservation of imperial gates; spruce fir wood; painting materials; This article is an open access article 3D scanning distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Appl. Sci. 2021, 11, 3422. https://doi.org/10.3390/app11083422 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, 3422 2 of 19

Appl. Sci. 2021, 11, 3422 2 of 18

1. Introduction 1. Introduction The central element of this paper is an interdisciplinary methodology, which em- The central element of this paper is an interdisciplinary methodology, which employs ploys state of the art , instruments, techniques, and equipment, found suitable by the state of the art tools, instruments, techniques, and equipment, found suitable by the authors, authors, for capitalizing on a heritage asset (namely, the wooden church of Voivodeni, for capitalizing on a heritage asset (namely, the wooden church of Voivodeni, Sălaj County, Sălaj County, Romania, (Figure 1), and the imperial gates from within (illustrated in Fig- Romania, (Figure1), and the imperial gates from within (illustrated in Figure2), through ure 2), through digital restoration/conservation and promotion to a wider audience. digital restoration/conservation and promotion to a wider audience. In this regard, in the specialty literature we find a series of examples that use various In this regard, in the specialty literature we find a series of examples that use various digital technologies for the digital restoration and conservation of various heritage sites, digital technologies for the digital restoration and conservation of various heritage sites, suchsuch as: as: city city centers centers [1], [ castles,1], castles or other, or other monuments monuments [2]. Furthermore, [2]. Furthermore, for studying for studying painted artefacts,painted artefacts, various techniques various techniques are used, suchare used, as: energy such dispersiveas: energy X-raydispersi spectroscopyve X-ray spectros- (EDX), polarizedcopy (EDX), light polarized microscopy light (PLM), microscopy X-ray (PLM), X-ray (XRD), diffraction micro-Raman (XRD), spectroscopy micro-Raman (m-RS),spectroscopy Fourier-transform (m-RS), Fourier -transform spectroscopy infrared (FTIR) spectroscopy and pyrolysis-gas (FTIR) and chromatography- pyrolysis-gas masschromatography spectrometry-mass (Py-GC/MS) spectrometry [3]; in(Py this-GC/MS) field, the[3]; texturein this field, obtained the texture by painters obtained when by usingpainters various when brushes using various and painting brushes techniques, and painting is also techniques, studied [ 4is]. also studied [4]. ThisThis paperpaper focusesfocuses onon the the “Holy “Holy Archangels Archangels Michael Michael and and Gabriel” Gabriel” wooden wooden church church fromfrom VoivodeniVoivodeni (Figure(Figure1 1),), whichwhich isis situated on on a a hill hill nearby nearby the the village, village, as astradition tradition dic- dictated,tated, and and was was constructed constructed from from dovetail dovetail joined joined wooden wooden beams. beams. The roof The has roof steep has angles, steep angles,and the and watchtower the watchtower is placed is on placed the roof on the ridge roof with ridge the with spire the that spire surpasses that surpasses the height the of heightthe walls. of the Inside walls. the Insidechurch the lies church an inscription lies an inscriptiondocumenting documenting the year when the construction year when constructionstarted: “It was started: appointed “It was for appointed the church for theto be church built to up be from built the up frommeadows the meadows in the year in the1820. year And 1820. it was And built it was at the built expense at the of expense the village, of the parish village, priest parish being priest Colciar being Ștefan Colciar with

S,histefan priest with son his Gheorghe priest son Ștefan, Gheorghe and S,thetefan, curator and thewas curator Elci Ioan. was And Elci the Ioan. holy And church the holy was

churchfinished was in the finished year 1822”. in the yearThe painter 1822”. Thewas painterthe priest was Iosif the Perșe priest from Iosif Elciu, Pers, e who from painted Elciu, whothis paintedchurch and this the church imperial and thegates imperial from within gates fromin the within year 1832 in the [5– year9]. 1832 [5–9]. TheThe FourFour Evangelists are are depicted depicted on on the the two two imperial imperial wooden wooden gates gates (Figure (Figure 2). Tra-2). Traditiondition assigned assigned a asymbol symbol to to each each of of them. them. Therefore, Therefore, Saint Saint Matthe Mattheww isis depicteddepicted togethertogether withwith aa manman (angel),(angel), SaintSaint MarcMarc isis depicted depicted together together withwith aa lion, lion, Saint Saint Luke Luke is is depicted depicted togethertogether withwith aa calf, calf, and and Saint Saint John John is is joined joined by by an an eagle. eagle. The The painting painting was was deteriorated deteriorated andand neededneeded immediate immediate preservation preservation and and restoration. restoration.

Figure 1. The wooden church of Voivodeni, Sălaj County, Romania. Figure 1. The wooden church of Voivodeni, Sălaj County, Romania. Appl. Sci. 2021, 11, 3422 3 of 19

Appl. Sci. 2021, 11, 3422 3 of 18

The investigation of the component materials (support materials and the painting layer) Thewas investigationcompleted through of the componentXRF and FTIR materials spectroscopic (support methods materials [10 and–16]. the The painting sam- plinglayer) points was completedfor XRF and through FTIR spectroscopy XRF and FTIR investigations spectroscopic are methods presented [10– 16in]. Figure The sampling 2. pointsBy employing for XRF and such FTIR physico spectroscopy-chemical investigations methods of investigation, are presented the in Figurepigments2. used in the constructionBy employing phase such are physico-chemicalidentified and documented, methods of because investigation, they represent the pigments the starting used in pointthe constructionin the classic phase restoration are identified operations and of documented, any historical because monument. they represent the starting pointFurthermore, in the classic in restoration order to contribute operations to of the any viability historical of monument.the investigated monument, the authorsFurthermore, propose ina method order to of contribute disseminating to the the viability results of based the investigated on cutting monument,edge technol- the ogiesauthors (namely, propose augmented a method and of disseminating virtual reality the—AR/VR). results based The onpopularization cutting edge of technologies this and other(namely, such augmentedmonuments, and based virtual on this reality—AR/VR). way of dissemination, The popularization may contribute of thisto their and rein- other troductionsuch monuments, into religious based and on thiscultural way oftourism dissemination, circuits, which, may contribute in term, towould their allow reintroduc- the collectiontion into and religious attraction and cultural of funds tourism necessary circuits, for their which, maintenance in term, would and allow restoration the collection (self- sustainment).and attraction of funds necessary for their maintenance and restoration (self-sustainment).

Yellow

Red

Green

Red

White

Blue

(a) (b)

FigureFigure 2. 2.TheThe Imperial Imperial Gates Gates of ofVoivodeni Voivodeni wooden wooden church church (a ()a and) and the the indication indication of of the the sampling sampling points points (b (b).). Appl. Sci. 2021, 11, 3422 4 of 19 Appl. Sci. 2021, 11, 3422 4 of 18

2. Materials and MethodsMethods The methodology (presented(presented inin FigureFigure3 3)) for for carrying carrying out out the the tasks tasks mentioned mentioned above above (documentation,(documentation, restoration, digitaldigital preservation,preservation, andand dissemination)dissemination) hashas beenbeen validatedvalidated on several types of artefacts and cultural heritage objects, originating fromfrom thethe church,church, andand itit beginsbegins withwith thethe documentationdocumentation fromfrom anan artisticartistic andand historicalhistorical pointpoint ofof viewview [[1515,,1717].].

Figure 3. Methodology.Methodology.

InIn the firstfirst part of the methodology, thethe artisticartistic andand historicalhistorical documentationdocumentation isis mademade by art historians and aims to certify the heritage valuevalue ofof thethe investigated monument.monument. ThisThis isis completedcompleted byby usingusing bibliographic,bibliographic, online,online, andand on-siteon-site sources.sources. The secondsecond stagestage consists consists of of the the photographic photographic documentation documentation of theof monument;the monument in this; in stagethis stage it is pursuedit is pursued the state-of-the-art the state-of-the documentation-art documentation and conservationand conservation of the of monument. the monu- Overviewment. Overview and detail and high detail resolution high resolution photos are photos taken, are in taken, both visible in both and visible invisible and spectrum invisible (IRspectrum or UV), (IR and or primaryUV), and information primary information is collected is for collected digitizing for thedigitizing monument. the monument. The three three-dimensional-dimensional ( (3D)3D) digitization digitization of of the the monument monument can can be becarried carried out out either ei- therby by photogrammetry or 3D orscanning, 3D scanning, depending depending on required on required resolution, resolution, allotted allottedtime for timescanning, for scanning, level of detail, level ofetc. detail, The textured etc. The 3D textured model 3Dshould model pre shouldsent the present current thestate cur- of rentconservation state of conservation as accurately as as accurately possible in as order possible to document in order to possible document future possible restoration future restoration interventions. interventions. The physico-chemical analyzes of the paint layer and the support materials should The physico-chemical analyzes of the paint layer and the support materials should identify the composition of the pigments and help to identify the problems in the painting’s identify the composition of the pigments and help to identify the problems in the paint- support: pests, fungi, etc. ing’s support: pests, fungi, etc. The identification of the pigments and their synthesis in the laboratory will determine The identification of the pigments and their synthesis in the laboratory will deter- the possible restoration operations, thus, it will be possible to choose compatible materials mine the possible restoration operations, thus, it will be possible to choose compatible and it will be possible to study the effect of the current materials used in the restoration of materials and it will be possible to study the effect of the current materials used in the the painting layer. After the pigment compositions are obtained, they can be digitized and restoration of the painting layer. After the pigment compositions are obtained, they can documented for the digital preservation of the monument. be digitized and documented for the digital preservation of the monument. The digital restoration operation aims to improve the visual appearance of the mon- The digital restoration operation aims to improve the visual appearance of the mon- ument in a virtual environment and to restore its appearance without any intervention (paintedument in layer a virtual I) or itsenvironment pristine appearance and to restore (painted its layerappearance 2—see) without from the any 1820s intervention (when the church(painted was layer built). I) or its pristine appearance (painted layer 2—see) from the 1820s (when the church was built). Appl. Sci. 2021, 11, 3422 5 of 19

Appl. Sci. 2021, 11, 3422 The digital restoration operation includes information from all stages described5 of 18 above: the scanned model is used to complete and remove the effects of time and other harmful factors on the monument, which is digitally repainted using digitized pigments obtainedThe digital from the restoration physico- operationchemical includesanalysis. informationOne can obtain from two all types stages of described 3D models, above: one therepainted scanned with model the isinitial used colors to complete and the and other remove one pai thented effects with of the time current and other colors. harmful factorsBy on going the monument, through the which stages is described digitally repaintedso far, a data using package digitized is obtained pigments that obtained corre- fromsponds the to physico-chemical the consolidated analysis. digital preservation One can obtain model two, types and which of 3D models,contains one the repaintedfollowing withinformation: the initial colors and the other one painted with the current colors. By going through the stages described so far, a data package is obtained that corresponds  Historical and artistic analysis; to the consolidated digital preservation model, and which contains the following information:  Complete photographic documentation of the monument; •  HistoricalDocumentation and artistic of the analysis; pigments and the state of conservation of the support of the • Complete photographic documentation of the monument; pictorial layer; • Documentation of the pigments and the state of conservation of the support of the  3D model of the monument; pictorial layer;  Digitally restored 3D model. • 3D model of the monument; • DigitallyAfter the restored completion 3D model. of the consolidated data package, some elements of it can be further used for the online promotion of the monument both on-site (through AR appli- After the completion of the consolidated data package, some elements of it can be fur- cations or audio guided tours) and remotely (through VR-type applications—virtual ther used for the online promotion of the monument both on-site (through AR applications tours). or audio guided tours) and remotely (through VR-type applications—virtual tours). The main goal of the previously described methodology is to preserve and digitally The main goal of the previously described methodology is to preserve and digitally restore monuments in various stages of degradation. This approach is interdisciplinary, restore monuments in various stages of degradation. This approach is interdisciplinary, basedbased on on techniques techniques from from various various fields fields of of engineering, engineering, and and is is presented presented as as follows. follows.

2.1.2.1. X-rayX-rayFluorescence Fluorescence Non-destructiveNon-destructive X-rayX-rayfluorescence fluorescence elemental elemental analysis analysis (XRF) (XRF) was was performed performed with with a a handheldhandheld Bruker Bruker spectrometer spectrometer (as (as shown shown in Figurein Figure4), S14), TITAN S1 TITAN series series (EDXRF) (EDXRF) configured config- withured a with Silicon a Silicon diode PIN diode detector PIN detector (SiPIN), Rh(SiPIN), target Rh X-ray target tube X with-ray atube maximum with a voltagemaximum of 50voltage kV. The of use50 kV. of this The approach use of this is approach validated is in validated various studies, in various as well studies, [18– 20as]. well [18–20].

Figure 4. X-ray In-Situ investigation. Figure 4. X-ray In-Situ investigation.

2.2.2.2. FTIRFTIR SpectroscopySpectroscopy Fourier-transformFourier-transformInfrared Infrared(FTIR) (FTIR)measurements measurementswere were performed performed with with a a Jasco Jasco 6100 6100 spectrometerspectrometer in in the the 4000 4000 to to 400 400 cm cm−1−1spectral spectral range range with with a a resolution resolution of of 4 4 cm cm−1−1 (256(256 scans)scans) byby employingemploying severalseveral (<1)(<1) mgmg ofof sample, sample, and and KBr KBr pellet pellet technique technique was was applied. applied. Similar Similar investigationsinvestigations are are detailed detailed in in other other research research endeavors, endeavors, as as well well [ 18[18,21,21].]. The The obtained obtained FTIR FTIR spectra were processed with the Spectral Analysis and the Origin 8.0 software. The samples were independently collected from the imperial gates and from mural paintings. Appl.Appl. Sci. Sci. 2021 2021, 11,, 113422, 3422 6 of6 of19 19

Appl. Sci. 2021, 11, 3422 spectraspectra were were processed processed with with the the Spectral Spectral Analysis Analysis and and the the Origin Origin 8.0 8.0 software. software. The The sam- sam-6 of 18 plesples were were independently independently collected collected from from the the imperial imperial gates gates and and from from mural mural paintings. paintings.

2.3.2.3.2.3. Digitization Digitization Digitization TheTheThe scanning scanning scanning and and and digitization digitization of ofthe thethe imperial imperialimperial gates gatesgates are areare aiming aiming aiming to to topreserve preserve preserve the the the con- conser- con- servationservationvation status status status in in inan an an electronic electronic electronic format. format. format. The The The 3D 3D 3D model modelmodel is isfurtheris furtherfurther used used for for various various research research research activitiesactivitiesactivities and and and also also also for for forthe the thepromotion promotion promotion of ofthese of these these patrimony patrimony patrimony assets. assets. assets. The The The digitization digitization digitization was was was per- per- per- formedformedformed using using using a Creaform a a Creaform Creaform Go!SCAN Go!SCAN Go!SCAN 50 50structured 50 structured structured light light light sca sca scannernnernner with with with a 50 a a 50μm 50 μmµ dimensionalm dimensional dimensional precisionprecisionprecision able able able to toacquire to acquire acquire textures textures textures up up upto to268 to 268 268 Mpx. Mpx. Mpx. The The The digitization digitization digitization operation operation operation targeted targeted targeted both both both thethe theshape shape shape and and and texture texture texture of ofthe of the thegates, gates, gates, the the thedata data data being being being acquired acquired acquired simultaneously. simultaneously. simultaneously. TheTheThe 3D 3D mesh 3D mesh mesh resulted resulted resulted from from fromscanning scanning scanning has has approximately has approximately approximately 4 mill 4 million 4ion million polygons/gate polygons/gate polygons/gate (Fig- (Fig- ureure(Figure 5b), 5b), which 5whichb), whichwere were further were further further transformed transformed transformed to toa surface a surface to a surface on on which which on the which the texture texture the texture(Figure (Figure (Figure5a) 5 wasa) was5 a) remapped.remapped.was remapped. The The Imperial Imperial The Imperial Gate Gate surface Gatesurface surface and and the andthe final final the 3D final 3D model model 3D modelare are presented arepresented presented in inFigure Figure in Figure 6. 6. 6.

(a)( a) (b)( b) FigureFigureFigure 5. The5. 5. TheThe texture texture texture (a) (anda (a) )and and the the themesh mesh mesh resulted resulted resulted from from from processing processing processing (b )(. ( bb))..

(a)( a) (b)( b)

FigureFigureFigure 6. The6. 6. TheThe Imperial Imperial Imperial Gate’s Gate’s Gate’s surface surface surface (a) (anda (a) )and and the the thefinal final final three three three-dimensional-dimensional-dimensional (3D ( (3D)3D) model) model model (b )(. ( bb)).. Appl. Sci. 2021, 11, 3422 7 of 19

Appl. Sci. 2021, 11, 3422 7 of 18

3. Results and Discussion 3. ResultsIn the and following, Discussion the results obtained from deploying the methodology are presented, detailedIn the, following,and applied the by results an interdisciplinary obtained from deployingteam of chemists, the methodology theologians, are presented,graphic art- detailed,ists, artand historians, applied engineers by an interdisciplinary, and IT specialists. team of The chemists, stages theologians,of physico-chemical graphic artists,analysis artand historians, digitization engineers, of the monum and IT specialists.ent take place The in stages parallel, of physico-chemicalthe completion of analysisthe two stages and digitizationcondition the of thetransition monument to thetake digital place restoration in parallel, stage. the completion of the two stages condition the transition to the digital restoration stage. 3.1. Artistic and Historical Documentation 3.1. Artistic and Historical Documentation An element of these monuments, distinguished by its symbolic significance, are the imperialAn element gates. ofThese these are monuments, essential components distinguished of the by itsiconostasis symbolic of significance, the Orthodox are Chris- the imperialtian churches, gates. These with symbolic are essential value components for cultural of heritage. the iconostasis Byzantine of the iconography Orthodox Christian associates churches,with the with imperial symbolic gates value the icon for cultural of the Annunciation, heritage. Byzantine as the iconography initial moment associates of saving with hu- themanity, imperial through gates thethe iconsymbolic of the opening Annunciation, of the gates as the of initial Heaven moment by Jesus. of saving humanity, throughIn the the symbolic Romanian opening Orthodox of the gates tradition, of Heaven the transcendental by Jesus. passageway is made throughIn the three Romanian symbolic Orthodox gates, tradition,through three the transcendental levels of access: passageway the entrance is made to the through precinct, threethe symbolicaccess gate gates, to the through church three and levels the imperial of access: gates, the entranceaccessible to to the priests. precinct, They the separate access gatethe to altar the churchfrom the and nave. the imperialDue to the gates, size accessible of the wooden to priests. churches They separate from Transylvania, the altar from the the nave. Due to the size of the wooden churches from Transylvania, the imperial gates imperial gates tend to take on greater importance in the eyes of the faithful. tend to take on greater importance in the eyes of the faithful. Following the field study conducted between 2016 and 2019, it was found that the Following the field study conducted between 2016 and 2019, it was found that the best best preserved are those churches that are still functional. The depopulation of rural areas preserved are those churches that are still functional. The depopulation of rural areas has has reduced their number every year. Some of the inactive churches were saved by con- reduced their number every year. Some of the inactive churches were saved by converting verting them to open-air village museums. Moreover, valuable artefacts were saved by them to open-air village museums. Moreover, valuable artefacts were saved by moving moving them to these museums. them to these museums. Of the 68 wooden churches from Sălaj County, Romania (including the three Of the 68 wooden churches from Sălaj County, Romania (including the three churches churches that were moved to open-air museums in Sibiu and Cluj-Napoca), only 21 pre- that were moved to open-air museums in Sibiu and Cluj-Napoca), only 21 preserve imperial serve imperial gates, among which is also the church in Voivodeni. gates, among which is also the church in Voivodeni. In this stage, a photographic documentation is carried out, in both the visible and In this stage, a photographic documentation is carried out, in both the visible and invisibleinvisible spectrum spectrum (IR (IR and and UV), UV), asas shownshown in Figure 77.. The The purpose purpose of of this this stage stage is isto tocap- captureture the the current current state state of ofconservation conservation (visible (visible spectrum) spectrum) and and possible possible interventions interventions or even or evenhelpful helpful sketches sketches used used during during the thepainting painting process process by folk by folk artists. artists. TheThe photographic photographic documentation documentation is is constituted constituted in in a documenta document that that will will preserve preserve in in digitaldigital format format the the current current state state of of conservation conservation of of the the monument. monument. DSLR DSLR cameras cameras (Canon (Canon 5DSR—50Mpx)5DSR—50Mpx) and and a multispectrala multispectral camera camera (modified (modified Canon Canon 550—18Mpx) 550—18Mpx) were were used used to to completecomplete this this documentation. documentation.

FigureFigure 7. 7.Photographs Photographs of of Imperial Imperial Gates Gates in in the the visible visible and and IR IR spectrum. spectrum.

InIn Figure Figure7, the7, the first first two two images images provide provide an an overview overview of theof the whole whole artefact, artefact, while while the the lastlast two two showcase showcase a close-upa close-up on on the the top top right right area. area. Appl. Sci. 2021, 11, 3422 8 of 19 Appl. Sci. 2021, 11, 3422 8 of 18

3.2.3.2. DigitizationDigitization TheThe woodenwooden churchchurch hashas beenbeen scannedscanned usingusing aa terrestrialterrestrial laserlaser scannerscanner (Z(Z ++ FF 5010x)5010x) toto obtainobtain anan accurateaccurate coloredcolored pointpoint cloudcloud ofof thethe church’schurch’s interiorinterior andand exteriorexterior (Figure(Figure8 8).). TheThe vastvast majoritymajority ofof digitaldigital reconstructionsreconstructions areare basedbased onon 3D3D modelsmodels createdcreated inin variousvarious software,software, butbut thethe accuracyaccuracy ofof aa modelmodel generatedgenerated onon aa computer,computer, whichwhich is is basedbased onon aa layoutlayout sketchsketch ofof thethe woodenwooden churchchurch willwill notnot havehave thethe requiredrequired accuracyaccuracy inin termsterms ofof geometricalgeometrical dimensions.dimensions. Therefore,Therefore, mostmost digitaldigital reconstructionreconstruction modelsmodels forfor culturalcultural heritageheritage assetsassets areare basedbased onon approximations.approximations. ByBy usingusing aa state-of-the-artstate-of-the-art terrestrialterrestrial laserlaser scanner,scanner, itit enablesenables aa truetrue 1:11:1 scale scale digital digital recreation recreation of of the the entire entire church church (both (both interior interior and and exterior) exterior) also thealso part the involvingpart involving the texturizing the texturizing process process is done is done automatically automatically and accurately, and accurately, since since the scanner the scan- is capablener is capable to acquire to acq theuire data the as data a colored as a colored point cloud point (XYZRGBcloud (XYZRGB file extension). file extension).

FigureFigure 8.8. VoivodeniVoivodeni woodenwooden churchchurch pointpoint cloudcloud andand itsits surroundings,surroundings, resulted resulted from from 3D 3D scanning. scanning.

3.3. XRF 3.3. XRF The purpose of the EDX-XRF spectroscopy was to determine the pigments from the The purpose of the EDX-XRF spectroscopy was to determine the pigments from the painting materials; they are centralized in Table 1. The chemical elements of those pig- painting materials; they are centralized in Table1. The chemical elements of those pigments ments are detailed in Figure 9a–g. are detailed in Figure9a–g.

Table 1. Sampled colors from the imperial gates and identified pigments (based on Figure 9). Table 1. Sampled colors from the imperial gates and identified pigments (based on Figure9). Color XRF Spectrum/Figure Pigment Color XRF Spectrum/Figure Pigment White Figure 9a Lead white WhiteYellow Figure9aFigure 9b LeadOrpiment white Yellow Figure9b Orpiment GroundGround Figure9cFigure 9c CalciumCalcium salt basedsalt based RedRed Figure9dFigure 9d RedRed mercury mercury (cinnabar) (cinnabar) BlueBlue Figure9eFigure 9e AzuriteAzurite GreenGreen Figure9fFigure 9f MalachiteMalachite Red Figure9g Red iron Red Figure 9g Red iron Appl.Appl. Sci. Sci. 20212021,, 1111,, 3422 3422 9 9of of 19 18

(a) (b)

(c) (d)

(e) (f)

(g)

FigureFigure 9. 9. ChemicalChemical elements elements present present in in the the painting painting materials materials.. Appl. Sci. 2021, 11, 3422 10 of 19

Appl. Sci. 2021, 11, 3422 10 of 19 Appl. Sci. 2021, 11, 3422 10 of 18

3.4. FTIR Investigation of Imperial Gates Wood 3.4.3.4. FTIR FromFTIR Investigation Ithenvestigation comparison of of Imperial Imperial of FTIR Gates Gates spectrum Wood Wood of spruce fir with the FTIR spectrum of im- perialFromFrom gates the the(IG) comparisoncomparison wood, of the of FTIR frame spectrum spectrum wood, see of of spruceFigure spruce fir10 fir ,with especially with the the FTIR FTIRthe spectrum 1100 spectrum–900 ofcm im- of−1 imperialspectralperial gates range, gates (IG) (IG)spruce wood, wood, fir wasof of the the identified frame wood, as being seesee employed FigureFigure 10 10, for, especially especially the IG wood the the 1100–900 1100and –frame.900 cm cm− 1−1 spectralspectral range, range, spruce spruce fir fir was was identified identified as as being being employed employed for for the the IG IG wood wood and and frame. frame.

Figure 10. Imperial gates’ wood- and frame wood FTIR spectra (as compared to the spruce fir Figureone)Figure. 10. 10.Imperial Imperial gates’ gates’ wood- wood- and and frame frame wood wood FTIR FTIR spectra spectra (as (as compared compared to to the the spruce spruce fir fir one). one). 3.5. Painting MaterialsMaterials 3.5. ThePainting green M paintingpaintingaterials materialmaterial was was identified identified as as malachite malachite and and gypsum gypsum by by the the character- charac- − isticteristic absorptionsThe absorptions green painting located located atmaterial at ~3600–3400 ~3600 was–3400 identified and and 1200–1000 1200 as– 1000malachite cm cm−11,, respectively,and gypsum seeby the Figure charac- 11. Yellowteristic paintingpainting absorptions material material located was was at identified identified~3600–3400 by by XRFand XRF as1200 as being being–1000 orpiment. orpiment.cm−1, respectively, Egg Egg yolk yolk was see was identified Figure identi- 11. − byfiedYellow its by specific its painting specific absorptions material absorptions presentwas presentidentified in the~3000–2800 in bythe~3000 XRF as– and2800 being 1800–1500 and orpiment. 1800– cm1500 Egg1 spectralcm yolk−1 spectral was domains identi- do- (Figuremainsfied by ( Figure11 its). specific Red 11 and). Redabsorptions Burgundy and Burgundy paintingpresent painting in materials the~3000 materials were–2800 identified andwere 1800 identified as–1500 mixtures cm as−1 mixtures ofspectral red lead, do-of redmains iron,lead, (Figure andred iron red 11, mercury ).and Red red and mixedmercury Burgundy with mixed gypsum painting with (Figuregypsum materials 12 (Figure), basedwere 12 identified on), based XRF results. on as XRF mixtures results. of red lead, red iron, and red mercury mixed with gypsum (Figure 12), based on XRF results.

Figure 11. FTIR spectra of the painting materials, 4000 to 400 cm−−11 spectralspectral range range. . Figure 11. FTIR spectra of the painting materials, 4000 to 400 cm−1 spectral range. Appl.Appl. Sci. Sci. 2021 2021, ,11 11, ,3422 3422 1111 ofof 1919 Appl. Sci. 2021, 11, 3422 11 of 18

−1 FigureFigure 12.12. 12. FTIR FTIR spectra spectra of of the the painting painting materials, materials, 40004000 4000 toto to 400400 400 cmcm cm−−11 spectral spectral range, range, Oy Oy extended extended extended.. .

3.6.33.6..6. Blue Blue PigmentPPigmentigment ConsideringConsidering thethe the datadata data fromfrom from XRFXRF XRF andand and FTIR,FTIR, FTIR, (Figures( (FigureFigures s 1313 13 andand and 1414 14),),), oneone one cancan can identifyidentify identify tracestraces traces ofof azuriteazuriteazurite ororor malachite malachitemalachite mixedmixedmixed withwithwith gypsum,gypsum,gypsum, eggeggegg yolk,yolkyolk, ,and andand linen linenlinen oil oiloil in inin the thethe blue blueblue painting paintingpainting −1 −1 materialmaterial (identified (identified(identified absorptions absorptions at at 3600 3600 3600–3400––34003400 cm cm −1−1 for forfor gypsum, gypsum, gypsum, 2930 2930 2930 cm cm cm−1−1 for for linen forlinen linen oil oil and and oil −1 −1 andeggegg yolk, eggyolk, yolk, 1647 1647 1647 cm cm−1−1 cm egg egg yolk yolkegg protein, yolkprotein, protein, ~1100 ~1100 ~1100–1000––10001000 and and ~615 ~615 and–– ~615–580580580 cm cm−1−1 for cmfor gypsum). gypsum).for gypsum).

FigureFigure 13.13. 13. FTIR FTIR spectraspectra spectra ofof of variousvarious various blue blue blue and and and green green green painting p paintingainting materials, materials, materials, 4000 4000 4000 to 400to to 400 400 cm cm −cm1 −1spectral−1 spectral spectral range. rangerange. . Appl. Sci. 2021, 11, 3422 12 of 19 Appl. Sci. 2021, 11, 3422 12 of 18

FigureFigure 14.14. FTIR spectra spectra of of various various blue blue and and green green painting painting materials, materials, 2000 2000 to 400 to 400 cm cm−1 spectral−1 spectral range,range, extendedextended OyOy axis.axis.

4.4. DigitalDigital RestaurationRestauration andand VRVR EnvironmentEnvironment IntegrationIntegration ofof ImperialImperial GatesGates DigitalDigital conservationconservation ofof thethe imperialimperial gatesgates isis performedperformed byby storingstoring thethe followingfollowing data:data: • PrimaryPrimary datadata resultedresulted fromfrom scanningscanning andand photographingphotographing duringduring scanning;scanning; • DetailedDetailed 3D model resulted resulted from from processing processing data data acquired acquired by byscanning scanning without without ap- applyingplying data data reduction reduction filte filtersrs or or texture ; compression; • OptimizedOptimized 3D model model—this—this is is a acompressed compressed model model resulted resulted from from data data reduction reduction em- employingploying various various filtering filtering and and compressing compressing operations; operations; • AllAll the the physical physical and and chemical chemical tests tests performed performed on theon the painting painting layer layer and woodenand wooden support. sup- Theport. detailed 3D model of the imperial gates (see Figure6) has approximately 1.8 GB and itThe is difficultdetailed to3D be model accessed of the by imperial the public, gates being (see usedFigure mainly 6) has forapproximately research activities 1.8 GB andand digitalit is difficult restoration, to be accessed as shown by in the [12 ].public, Compressing being used using mainly various for research methods activities [22–25] aimsand digitalto obtain restoration, a simplified as 3D shown model in in [12 order]. Compressing for it to be visualized using various and methodsused on various[22–25] cross-platformaims to obtain devices.a simplified 3D model in order for it to be visualized and used on various crossA-platform virtual application devices. was created in Unity software (version 2020.2.0f1) for the imperial gates,A which virtual facilitates application their wa visualizations created in employingUnity software HTC (version Vive. The 2020.2.0f1) user can move for the around impe- theserial gates, artefacts which and facilitates can visualize their them on a 1:1 scale.employing HTC Vive. The user can move aroundBesides these this artefacts application, and can the visualize 3D model them is shared on a 1:1 on scale. the sketchfab.com platform where users can manipulate the 3D model and stereoscopically visualize the imperial gates using Besides this application, the 3D model is shared on the sketchfab.com platform where a smartphone and a headset. Using the facilities from this platform, the users can manipulate the 3D model and stereoscopically visualize the imperial gates using 3D models can be associated with a marker, visualized, and manipulated within the appli- a smartphone and a headset. Using the augmented reality facilities from this platform, the cation (Figure 15). The 3D model of the gates can be visualized at https://skfb.ly/6ZXqx 3D models can be associated with a marker, visualized, and manipulated within the ap- (published: 29 March 2021; accessed: 30 March 2021). plication (Figure 15). The 3D model of the gates can be visualized at https://skfb.ly/6ZXqx The process of preserving the current situation of the whole wooden church from (published: 29 March 2021; accessed: 30 March 2021). Voivodeni was one of the most important objectives of the research, but our research is also The process of preserving the current situation of the whole wooden church from focused on the potential use of digital image processing to recreate the paintings. As a case Voivodeni was one of the most important objectives of the research, but our research is study, the digital restauration has been applied on one of the four evangelists, namely, on also focused on the potential use of digital image processing to recreate the paintings. As Saint Marc (upper part of Figures2b and 16). The starting point for this step involves the a case study, the digital restauration has been applied on one of the four evangelists, use of the detailed 3D model, which had the precise 3D geometry as well as the mapped texturenamely, acquired on Saint using Marc the(upper hand-held part of Creaform Figures 2 Go!SCANb and 16). 50The structured starting point light for scanner. this step To obtaininvolves more the detailsuse of forthe thedetailed texture 3D of model, each Saint, which we had have the used precise a 50 3D Mpx geometry full frame as well DSLR as camerathe mapped to gather texture a close-up acquired of using the painting, the hand which-held Creaform was later Go!SCAN merged into 50 s atructured single digital light image.scanner. The To merged obtain more high detaileddetails for image the texture has been of usedeach asSaint, the startingwe have point used for a 50 the Mpx digital full frame DSLR camera to gather a close-up of the painting, which was later merged into a Appl. Sci. 2021, 11, 3422 13 of 19

Appl. Sci. 2021, 11, 3422 13 of 18 single digital image. The merged high detailed image has been used as the starting point for the digital restoration process. To have a better lighting over the painting, the wooden gatesrestoration were photographed process. To outside have a betterin natural lighting sunlight over and the artificial painting, light, the woodenfor a better gates expo- were sure.photographed outside in natural sunlight and artificial light, for a better exposure.

FigureFigure 15. 15.ShowcasingShowcasing the the imperial imperial gate gatess using using virtual virtual reality reality..

TheThe proposed proposed digital digital reconstruction reconstruction involved involved adjustment adjustment of the of color the color saturation saturation to betterto better illustrate illustrate the initial the initialsituation situation and colors and of colors the paintings. of the paintings. A wide variety A wide of variety digital of imagedigital manipulation image manipulation has been hasapplied been to applied recolor to the recolor missing the missingareas of areas the painting of the painting and addingand addingdetails detailswith various with variousbrush strokes, brush strokes,the proposed the proposed digital reconstruction digital reconstruction is high- is lightedhighlighted in Figure in 16 Figure. However, 16. However, here it must here be it mustnoted be that noted according that according to [26] virtual to [26 ]resto- virtual rationrestoration is the process is the process of “using of “usinga virtual a virtual model model to reorder to reorder available available material material remains remains to visuallto visuallyy recreate recreate something something that existed that existed in the inpast. the Thus, past. Thus,virtual virtual restoration restoration includes includes vir- tualvirtual anastylosis anastylosis”,”, which which in turn in turn“involves “involves restructuring restructuring existing existing but but dismembered dismembered parts parts in ain virtual a virtual model model”.”. Moreover, Moreover, because because these these techniques techniques are are deployed deployed in inthe the digital digital/virtual/virtual environmentenvironment they they do do not not interfere interfere with with the the materiality materiality of ofthe the original original artwork, artwork, thus thus virtual virtual restorationrestoration does does no nott contravene contravene with with well well-established-established principles principles of ofphysical physical restoration, restoration, suchsuch as ascompatibility, compatibility, reversibility, reversibility, or orminimal minimal intervention intervention [26,27 [26,].27 Finally,]. Finally, the the digitally digitally restoredrestored model model does does no nott claim claim to tohave have the the same same artistic artistic value value as asthe the original, original, its itspurpose purpose is tois toillustrate illustrate a probable a probable variant variant of ofthe the original original artwork, artwork, without without the the action action of ofdegrading degrading factorsfactors upon upon it [28,29 it [28,].29 ]. TheThe proposed proposed digital digital restoration restoration has has then then been been projected projected on onthe the 3D 3D model model obtained obtained usingusing the the 3D 3D handheld handheld structured structured light light scanner. scanner. To To generate generate a proposed digitaldigital restaurationrestaura- tionthe the whole whole right right side side of of thethe imperialimperial gate has has also also been been recolored recolored using using the the colors colors from from thethe chromatic chromatic pallet pallet of the of thedigital digital image image acquired acquired by the by structured the structured light scanner. light scanner. For ob- For obtaining the image from the right side of Figure 16, the colors used in the repainting taining the image from the right side of Figure 16, the colors used in the repainting process process are obtained in laboratory conditions, based on the pigments identified as presented are obtained in laboratory conditions, based on the pigments identified as presented in in Section 3.3, centralized in Table1. By doing so, one can assume that the artefact is colored Section 3.3., centralized in Table 1. By doing so, one can assume that the artefact is colored as its “pristine condition”—before it was affected by degrading (external) factors. The result as its “pristine condition”—before it was affected by degrading (external) factors. The re- of the recolored right side of the imperial gate is presented in the figure below, directly in a sult of the recolored right side of the imperial gate is presented in the figure below, directly 3D texturing software (Substance Painter) that enables UV unwrapping and texturing. in a 3D texturing software (Substance Painter) that enables UV unwrapping and texturing. In Figure 17, the 3D model and its material are presented, used for texturing purposes, in an unwrapped format; for the texture, a custom physically-based rendering (PBR)-type material was created, capable of reacting with the conditions from the virtual environment Appl. Sci. 2021, 11, 3422 14 of 19

Appl. Sci. 2021, 11, 3422 14 of 18

(lighting, shadows, reflections, etc.) and the mapping mode is “normal mapping”, which is a technology of changing a normal pixel based on the chorochromatic map of normals, in Appl. Sci. 2021, 11, 3422 which changing data are saved as texels. In this method, three texture channels are used14 of on 19

the map and, thanks to them, it has greater accuracy.

Figure 16. Proposed digital restoration of Saint Marc illustration on the imperial gates from Voi- vodeni.

In Figure 17, the 3D model and its material are presented, used for texturing pur- poses, in an unwrapped format; for the texture, a custom physically-based rendering (PBR)-type material was created, capable of reacting with the conditions from the virtual environment (lighting, shadows, reflections, etc.) and the mapping mode is “normal map- Figure 16. Proposed digital restoration of Saint Marc illustration on the imperial gates from Voi- Figureping”, 16.whichProposed is a technology digital of restoration changing of a normal Saint Marc pixel illustrationbased on the on chorochromatic the imperial gates map vodeni. fromof normals, Voivodeni. in which changing data are saved as texels. In this method, three texture chan- nels are used on the map and, thanks to them, it has greater accuracy. In Figure 17, the 3D model and its material are presented, used for texturing pur- poses, in an unwrapped format; for the texture, a custom physically-based rendering (PBR)-type material was created, capable of reacting with the conditions from the virtual environment (lighting, shadows, reflections, etc.) and the mapping mode is “normal map- ping”, which is a technology of changing a normal pixel based on the chorochromatic map of normals, in which changing data are saved as texels. In this method, three texture chan- nels are used on the map and, thanks to them, it has greater accuracy.

FigureFigure 17. 17.The The recolored recolored model model of of the the right-side right-side door door of of the the imperial imperial gates gates from from Voivodeni. Voivodeni.

TheThe resulting resulting 3D 3D models models of of the the imperial imperial gates gates from from Voivodeni Voivodeni have have been been included included in in aa virtual virtual reality reality application, application, which which is is dedicated dedicated to to the the imperial imperial gates gates from from Transylvania Transylvania (Cluj(Cluj and and S ăSălajlaj counties, counties, Romania). Romania). The The VR VR application application integrates integrates multiple multiple 3D 3D scanned scanned imperialimperial gates gates and and the the application application has has been been constantly constantly updated updated with with new new scans. scans. An An older older

version of the application has been presented in an article focused on the multidisciplinary Figure 17. The recolored model of the right-side door of the imperial gates from Voivodeni.

The resulting 3D models of the imperial gates from Voivodeni have been included in a virtual reality application, which is dedicated to the imperial gates from Transylvania (Cluj and Sălaj counties, Romania). The VR application integrates multiple 3D scanned imperial gates and the application has been constantly updated with new scans. An older Appl. Sci. 2021, 11, 3422 15 of 18

investigation of the imperial gate from Sălis, ca, Cluj county, Romania [15]. The applica- tion has been created using the Unity game engine software and it is compatible with a wide variety of head-mounted display (HMD) systems. The widespread adoption and compatibility with multiple VR systems have defined Unity as one of the most popular software solutions used to promote digital cultural heritage assets. The main advantage of transferring the 3D scanned model to virtual reality environments in comparison to other dissemination branches, such as webpage, is the ability to create interactive applications using a wide variety of sensors and controllers to manipulate or interact with the digital environment and allow users to fully immerse themselves (as showcased in this video: https://youtu.be/nnWSUrcDdZU---published: 8 March 2021; accessed: 9 March 2021). For the promotion of the imperial gates, the virtual reality application was designed to work with HTC Vive/Cosmos and Valve Index virtual reality systems (HMD). The software behind the virtual reality tracking and interaction is based on SteamVR Software Development Kit (SDK) and it can work with various configurations—with HTC Vive wireless system up to Cosmos Elite—which does not require base to track the user’s “virtual hands” as controllers. The proposed virtual reality application integrates multiple imperial gates, which are paired with various metadata. On the walls behind each imperial gate, there are images and text metadata regarding the individual location. For some wooden churches, there are also videos that present the location of the wooden church and details regarding the 3D digitization of it. The audio metadata files are positioned using a location bounding box; therefore, the user will be able to hear additional information regarding each individual wooden church and imperial gate, if he will be in the close proximity of those elements within the virtual environment. The figure below presents the location of the imperial gates from Voivodeni within the virtual environment. As can be observed, the left side of the imperial gates are the original models, as they have been obtained using 3D scanning, while for the ones in the right side, the digital reconstruction of Saint Marc is projected on top of the 3D scanned model, highlighting the difference between the original saturated colors of the painting and the current state. Unfortunately, for the imperial gates from Voivodeni, they have not been physically curated and repainted, but hopefully there will be funding for this process as well as the whole painting from the interior of the church. Until then, the process of creating digital restoration is being used to raise awareness and to highlight the importance of restoring these types of cultural heritage assets that are present in most villages from Transylvania. In Figure 18, to the left of the image, the imperial gates from Bulgari, Sălaj County, Ro- mania, are presented, both in their initial state (to the right of the screen) and in their physical restored version (to the left of the screen). Both models have been 3D scanned by the team in- volved within this project using the same structured light scanner—Creaform Go!SCAN 50. Another important feature of the virtual environment is based on the ability of the user to navigate the scene using the teleportation function. The system is capable of tracking the user in real time, but there are some limitations regarding the area where the users can move within the real environment, and the feature of teleportation helps to overcome this, easily. Teleportation can allow users to rapidly navigate the scene and to get close to the 3D scanned objects, allowing them to observe the detailed three-dimensional environment. Using this feature, the users can easily look at the models from the other side and in some cases on the back of the imperial gates there are various elements as, for example, the

imperial gates from Sânmihaiu Almas, ului, Sălaj County, have a text marking on the back, as well as the year 1816 (Figure 19). The virtual reality application’s camera tracking follows the position of the user, by default the camera is set in the middle of the virtual reality environment, where there is a table and three paintings. As soon as the user raises the HMD, the height of the camera will adjust to the user. Some of the imperial gates are above 2 m height, and some users, such as small children, may encounter problems when they try to spot various details on upper Appl. Sci. 2021, 11, 3422 16 of 18

side of the gates; therefore, they can use the fly mode with the help of the controllers (by pressing two button—one for up and one for down), which enables them to ascend above Appl. Sci. 2021, 11, 3422 the ground floor in the virtual reality environment. At a height of 4 m, there is a collision16 of 19 box, which keeps the user from elevating at a higher distance from the floor, keeping the users within the designated visualization environment. A short video, illustrating the way in which a user interacts with the objects from the virtual environment, being fully immersed in it using an HMD, can be found at the Appl. Sci. 2021, 11, 3422 16 of 19 following link: https://youtu.be/nnWSUrcDdZU (published: 8 March 2021; accessed: 9 March 2021).

Figure 18. The imperial gates from Voivodeni positioned within the virtual reality environment.

Using this feature, the users can easily look at the models from the other side and in some cases on the back of the imperial gates there are various elements as, for example, the imperial gates from Sânmihaiu Almașului, Sălaj County, have a text marking on the Figure 18. The imperial gates from Voivodeni positioned within the virtual reality environment. Figureback, 18.as wellThe imperialas the year gates 1816 from (Figure Voivodeni 19). positioned within the virtual reality environment. Using this feature, the users can easily look at the models from the other side and in some cases on the back of the imperial gates there are various elements as, for example, the imperial gates from Sânmihaiu Almașului, Sălaj County, have a text marking on the back, as well as the year 1816 (Figure 19).

Figure 19. The imperial gates from Sânmihaiu Almașului, Sălaj County, back details. Figure 19. The imperial gates from Sânmihaiu Almas, ului, Sălaj County, back details.

5. ConclusionsThe virtual reality application’s camera tracking follows the position of the user, by defaultUsing the ancamera interdisciplinary is set in the middle approach, of the based virtual on reality physico-chemical environment, analysis where there and 3D is a table and three paintings. As soon as the user raises the HMD, the height of the camera digitizationFigure 19. The techniques, imperial gates long-term from Sânmihaiu digital preservationAlmașului, Sălaj is C possibleounty, back with details an information. package,will adjust which to the provides user. Some an overview of the imperial and accurate gates are data above about 2 m the height, imperial and gates. some Afterusers, such as small children, may encounter problems when they try to spot various details on identifyingThe virtual and documenting reality application’s the heritage camera asset, tracking the interdisciplinary follows the position team of carried the user, out aby upper side of the gates; therefore, they can use the fly mode with the help of the controllers massivedefault in-situthe camera data is collection, set in the whichmiddle includes of the virtual physico-chemical reality environment, analyzes where for each there color is a (by pressing two button—one for up and one for down), which enables them to ascend table and three paintings. As soon as the user raises the HMD, the height of the camera above the ground floor in the virtual reality environment. At a height of 4 m, there is a will adjust to the user. Some of the imperial gates are above 2 m height, and some users, collision box, which keeps the user from elevating at a higher distance from the floor, such as small children, may encounter problems when they try to spot various details on keeping the users within the designated visualization environment. upper side of the gates; therefore, they can use the fly mode with the help of the controllers (by pressing two button—one for up and one for down), which enables them to ascend above the ground floor in the virtual reality environment. At a height of 4 m, there is a collision box, which keeps the user from elevating at a higher distance from the floor, keeping the users within the designated visualization environment. Appl. Sci. 2021, 11, 3422 17 of 18

(performed in different sampling places), 3D digitization of the monument and of the imperial gates, and artistic and historical documentation. The physico-chemical analyzes revealed that the woods used to craft the imperial gates and their frame are spruce fir and the component materials used in the painting process are ground gypsum; binder—egg yolk; red painting material—-red iron, red lead, red mercury; yellow—orpiment; green—malachite; blue—azurite; white—lead white; egg yolk painting technique. All of these results can further be used in the restoration of the entire monument and, at the same time, they are digitally preserved and stored together with all of the artistic and historical information, with the 3D model of the church and of the imperial gates, in their current state. The digital restoration of the imperial gates can be carried out using the pigments identified by the physico-chemical analyzes, applied on the 3D model of the church and the imperial gates. The later ones can be repainted with their current colors (painted layer I) or with the initial colors (from their pristine state), obtained by synthesizing them in the laboratory, based on the pigments identified in the painted layer (painted layer II). The 3D models can be used in virtual reality applications, which allow access to a much larger number of potential stakeholders, than in-situ visiting, and in the particular case of the imperial gates, allows the general public to see also the backside of the gates, which within the church is forbidden to female persons. Increasing the number of users who can examine the models and interact with them, the “appetite” of visitors for such cultural assets can be stimulated; thus, their reintroduction into the cultural and religious tourist circuits can be achieved. Finally, it is worth mentioning that the methodology presented in this paper was vali- dated by the authors on five different imperial gates, with various particularities (such as the sculpting complexity—Figure 19—or with multiple painting layers—) being presented in the developed VR application (its fundamentals and practicalities were detailed in the previous section).

Author Contributions: Conceptualization, C.N., I.B., C.M. and D.P.; methodology, C.N., D.P., R.C.,

S, .B. and Z.B.; software, V.C.M., O.F.N., R.C., S, .B., D.P. and Z.B.; validation, C.N., V.C.M. and O.F.N.;

formal analysis, V.C.M., O.F.N., R.C., S, .B., D.P. and Z.B.; investigation, V.C.M. and O.F.N.; resources,

C.N., D.P., R.C. and S, .B.; data curation, V.C.M. and O.F.N.; writing—original draft preparation, C.N.,

V.C.M., S, .B. and R.C.; writing—review and editing, C.N., S, .B. and R.C.; visualization, C.N., R.C.,

S, .B. and Z.B.; supervision, C.N., I.B., C.M. and D.P.; project administration, C.N., I.B., C.M. and D.P.; funding acquisition, C.N. and D.P. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by a grant from the Romanian Ministry of Research and In- novation, CCCDI—UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0812/53PCCDI, within PNCDI III. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

References 1. Rossato, L.; Massai, P.; Maietti, F.; Balzani, M. Digital Tools for Documentation and Analysis of Vernacular Cultural Heritage in Indian City Centers. Int. J. Archit. Herit. 2019.[CrossRef] 2. García-Molina, D.F.; González-Merino, R.; Rodero-Pérez, J.; Carrasco-Hurtado, B. 3D Documentation for the Conservation of Historical Heritage: The Castle of Priego de Córdoba (Spain). Virtual Archaeol. Rev. 2020, 12, 115–130. [CrossRef] 3. Peng, F.; Ge-Le, T.; Jing, L.; Jia-Xin, L.; Yu-Hu, L.; Hong, Y. Investigation of Ancient Architectural Painting from the Taidong Tomb in the Western Qing Tombs, Hebei, China. Coatings 2020, 10, 688. [CrossRef] 4. Mironova, A.; Robache, F.; Deltombe, R.; Guibert, R.; Nys, L.; Bigerelle, M. Digital Cultural Heritage Preservation in Art Painting: A Surface Roughness Approach to the Brush Strokes. Sensors 2020, 20, 6269. [CrossRef] Appl. Sci. 2021, 11, 3422 18 of 18

5. Cristache-Panait, I. Biserica Sf. Arhangheli Mihail s, i Gavril din Voivodeni. Monumente istorice biserices, ti din Eparhia Ortodoxă Română a Oradei. Biserici de lemn; The Romanian Orthodox Episcopy of Oradea: Oradea, Romania, 1978; pp. 430–432. 6. Cristache-Panait, I. Bisericile de lemn din Sălaj. Buletinul Monumentelor Istorice 1971, 1, 31–40. 7. Ghergariu, L. Biserici de lemn din Sălaj; MSS in National Archives of Zalău, Personal Collection of Ghergariu Leontin, act 11 of 1976; National Archives of Zalău: Zalău, Romania, 1976.

8. Mărut, oiu, C.; Popescu, D.; Bratu, I.; Moraru, R.; Postolache, D.L. Biserici de lemn din Transilvania; Mega: Cluj-Napoca, Romania, 2017; ISBN 978-606-543-857-6.

9. Drăgu¸t,V. Dic¸tionarEnciclopedic de Artă Medievală Românească; Editura S, tiint, ifică s, i Enciclopedică: , Romania, 1976; pp. 35–36.

10. Nemes, , O.F.; Bratu, I.; Mărut, oiu, C.; Postolache, D.L.; Dragomir, M.; Tănăselia, C.; Garabagiu, S. Scientific Investigations of the Imparial Gates from Petrindu Wooden Church, Sălaj County, Romania. X-ray Spectrom. 2018, 47, 176–185.

11. Mărut, oiu, C.; Bratu, I.; Nemes, , O.F.; Dit, I.-I.; Comes, R.; Tănăselia, C.; Fălămas, , A.; Miclăus, M.; Marutoiu, V.C.; Moraru, R. Instrumental Analysis of Materials and Topology of the Imperial Gates Belonging to the Apahida Wooden Church, Cluj County. Vibr. Spectrosc. 2017, 89, 131–136. [CrossRef]

12. Bratu, I.; Siluan, M.; Mărut, oiu, C.; Kacso, I.; Garabagiu, S.; Mărut, oiu, V.C.; Tănăselia, C.; Popescu, D.; Postolache, D.L.; Pop, D. Science Applied for the Investigation of Imperial Gate from Eighteenth Century Wooden Church of Nicula Monastery. J. Spectrosc. 2017.[CrossRef]

13. Moldovan, Z.; Bratu, I.; Mărut, oiu, C.; Kacso, I.; Trosan, L.; Pop, D.; Nemes, , O.F.; Tănăselia, C. Characterization of an Eighteenth- Century Wooden Icon from the Ethnographic Museum of Transylvania. Anal. Lett. 2016, 49, 2597–2605. [CrossRef]

14. Hernanz, A.; Bratu, I.; Mărut, oiu, O.F.; Mărut, oiu, C.; Gavira-Vallejo, J.M.; Edwards, H.G.M. Micro-Raman Spectroscopic Investigation of External Paintings from St. Dumitru’s Church, Suceava, Romania. Anal. Bioanal. Chem. 2008, 392, 263–268. [CrossRef][PubMed]

15. Neamt, u, C.; Mărut, oiu, V.C.; Bratu, I.; Mărut, oiu, O.F.; Mărut, oiu, C.; Chirilă, I.; Dragomir, M.; Popescu, D. Multidisciplinary

Investigation of the Imperial Gates Belonging to the 17th Century Wooden Church of Sălis, ca, Cluj County, Romania. Sustainability 2018, 10, 1503. [CrossRef] 16. Gomes, L.; Bellon, O.R.P.; Silva, P. methods for digital preservation of cultural heritage: A survey. Pattern Recognit. Lett. 2014, 50, 3–14. [CrossRef]

17. Mărut, oiu, C.; Bratu, I.; Nemes, , O.; Nemes, , D.; Neamt, u, C.; Moldovan, Z.; Tia, T.; Udrea, I.; Tigae, C. Scientific investigation of the paintings from the Agârbiciu (Cluj County) Wooden Church. J. Min. Mat. Charact. Eng. 2020, 8, 177–196. [CrossRef] 18. Zamboni, C.B.; Redígolo, M.M.; Miura, V.T.; Costa, I.; Nagai, M.L.E.; Salvador, P.A.V.; Nogueira da Silva, D.G. Non-Destructive Analysis in the Study of Historical Photographs by pXRF and ATR-FTIR . J. Forensic Sci. 2021.[CrossRef] 19. Molari, R.; Appoloni, C.R.; Hennen Rodriguez, S. Non-Destructive Portable X-ray Fluorescence Analysis of the Portrait of a Young Man with a Golden Chain (c. 1635) by Rembrandt and/or Atelier. Appl. Radiat. Isot. 2020, 165.[CrossRef] 20. Hennen Rodriguez, S.; Appoloni, C.R.; Campos, P.H.O.V.; Gonçalves, B.; Kajiya, E.A.M.; Molari, R.; Rizzutto, M.A.; Winter, C. Non-Destructive and Portable Analyses Helping the Study and Conservation of a Saraceni Copper Plate Painting in the São Paulo Museum of Art. Microchem. J. 2020, 155. [CrossRef] 21. Retko, K.; Legan, L.; Ropret, P. SERS Procedure Using Photoreduced Substrates and Reflection FTIR Spectroscopy for the Study of Natural Organic Colourants. J. Raman Spectrosc. 2021, 52, 130–144. [CrossRef]

22. Neamt, u, C.; Popescu, D.; Mateescu, R.; Suciu, L.; Hurgoiu, D. About Quality and Properties of Digital Artifacts. Mediterr. Archaeol. Archaeom. 2014, 14, 55–64. 23. Hatzopoulos, J.N.; Stefanakis, D.; Georgopoulos, A.; Tapinaki, S.; Pantelis, V.; Liritzis, I. Use of Various Technologies to 3D Digital Mapping and Modelling of Cultural Heritage Structures for Maintenance and Restoration Purposes: The Tholos in Delphi, Greece. Mediterr. Archaeol. Archaeom. 2017, 17, 311–336. [CrossRef]

24. Comes, R.; Tompa, V.; Bodi, S, .; Neamt, u, C.; Torok, K.F. From Theory to Practice: Digital Reconstruction and Virtual Reality in Archaeology. J. Anc. Hist. Arch. 2018, 4, 80–88. [CrossRef] 25. Jamhawi, M.; Alshawabkeh, Y.; Freewan, A.; Al-Gharaibeh, R. Combined Scanner and Dense Stereo Matching Techniques for 3D Modelling of Heritage Sites: Dar Es-Saraya Museum. Mediterr. Archaeol. Archaeom. 2016, 16, 185–192. [CrossRef] 26. Lopez-Menchero, V.M.; Grande, A. The Principles of the Seville Charter. In Proceedings of the XXIInd CIPA Symposium, Prague, Czech Republic, 12–16 September 2011. 27. Xu, J.; Ding, L.; Love, P.E.D. Digital Reproduction of Historical Building Ornamental Components: From 3D Scanning to . Autom. Constr. 2017, 76, 85–96. [CrossRef] 28. Vico, L. Authenticity and Realism: Virtual vs. Physical Restoration. In Authenticity and Cultural Heritage in the Age of 3D Digital Reproductions; Di Giuseppantonio Di Franco, P., Galeazzi, F., Vassallo, V., Eds.; McDonald Institute: Cambridge, UK, 2018; pp. 25–33. [CrossRef] 29. Limoncelli, M. Virtual Hıerapolıs. Virtual Archaeology and Restoration Project (2007–2015), Hierapolis di Frigia XIII; Ege Yayinlari: Istanbul, Turkey, 2019; ISBN 978-605-7673-10-7.