Bulletin of the Transilvania of Bra şov • Vol. 3 (52) - 2010 Series II: • • Agricultural Food

MICROSCOPIC CHARACTERISATION OF FOUR EXOTIC SPECIES FOR HISTORIC CONSERVATION

L. GUR ĂU1 M.C. TIMAR 1 M. POROJAN 1 A. OL ĂRESCU 1

Abstract: Wood species identification is a compulsory step in the scientific conservation of the historic furniture. A visual examination of an investigated sample does not always bring enough information about the original species and a microscopic approach is more reliable. This paper is providing the microscopic characterisation with identification keys for four exotic species used in historic furniture. They can serve for wood identification purposes in the laboratories working in the field of wood cultural heritage conservation.

Key words: microscopy, wood identification, historic furniture, conservation.

1. Introduction involves in a first instance a macroscopic analysis of the wood part to identify its Furniture history goes back to the main features. Although sometimes a Antiquity and evolved as an important part careful macroscopic examination of a of the human and [1], clean transparently finished surface or a [2]. The ingenuity of structures, elegance freshly sanded surface is solving the of shapes, skilfulness of decoration and problem, there are many cases when a diversity of finishing techniques employing microscopic investigation is needed and natural materials are to be remarked and reference microscopic samples are employed many historic furniture objects remained for comparison and identification. Wood known as appreciated objects of art from species identification is based on the both aesthetical and technical point of characteristic macroscopic and microscopic view, continuing to be a valuable source of structural features included in an identification historic information. key. Given the variety of wood species that The paper is referring to such microscopic have been used in furniture history being characterization for four exotic species, employed from ancient to modern times, American - Swietenia macrophylla any restoration intervention that involves King, African mahogany - Khaya ivorensis wood completion or a replacement should A. Chev., wenge - Milletia laurentii De be very well documented and in Wild. and eucalypt - globulus accordance with the original material. This Labill ., to be used for wood identification

1 Dept. of Wood , Transilvania University of Bra şov.

124 Bulletin of the Transilvania University of Bra şov • Vol. 3 (52) - 2010 • Series II purposes by the laboratories working in the finishing with 100%. After this, sections field of wood cultural heritage conservation. were permanently mounted on glass slides, This is part of a recent research project one for each prism, by using a mountant aiming at developing and implementing a with refractive index close to that of glass: scientific investigation in furniture dried Canada balsam dissolved in xylene conservation [7]. [4]. By positioning the cover slip, the slides were gently pressed with a rubber tip 2. Methodology to uniform the spread of mountant and to remove air bubbles from inside. The Reference microscopic samples were mountant was then allowed to cure by produced as aids for species identification storing the slides for a few days in a warm during the further conservation activities of environment at 60 °C. Finally, the surplus any historic furniture. The work principle of Canada balsam was removed with a consists in comparing the microscopy of razor blade and the slides were cleaned and wood samples prelevated from the historic polished with a cloth and a little xylen artwork with a complete set of reference before labelling. images produced in this research as well as From each slide were taken several with the descriptions that accompany those images on each section at magnifications images and which are meant to guide the of 40x, 100x and 200x by means of an user towards features identification. optical BIOSTAR OPTECH The selection of species was based on B5 fitted with an image capture system. the knowledge regarding some of the The features of interest used also as keys commonly used wood in historic furniture: of identification for those species were: American mahogany - Swietenia macrophylla • The presence of pores, which is the King, African mahogany - Khaya ivorensis essential indicator of a species A.Chev., wenge - Milletia laurentii De compared to where they are Wild. and eucalypt - Eucalyptus globulus absent. The pores appear as holes of Labill. various magnitude on the cross sections In order to produce the reference and with a specific . They are microslides all materials above were rather uniformly spread in the growth areas conditioned by storing in a controlled if they are diffuse-porous (Figure 1). environment (20 °C and 65% relative air • The pores size is also important in humidity). Then two prisms of 30 × 10 × differentiating between species: some, with 10 mm were cut out of each type of diameters less than 100 µm can be very material. They were then boiled in flasks small visible only with the magnifying with refluxing condenser until saturated glass and easily distinguishable with the (about 24 hours). The prisms were microscope and those visible with the naked trimmed to expose the transverse, radial eye from 101 to over 300 even 500 µm. and tangential surfaces. Sections were cut • The pores arrangement and their from each surface with a sledge microtome proportion are other type of information to 25 micron thickness. solution which is looked for, as they can be solitary was used to prevent surface tension bounded entirely by other cell types attaching the sections to the knife. To (Figure 1 - C); can appear as a characteristic enhance the contrast, the sections were group of pores in the latewood or can be coloured with safranine solution and then multiple pores when two or several washed thoroughly in baths of ethanol features are disposed as radial arrangement solution of increasing concentration, (Figure 1- D).

Gur ău, L., et al.: Microscopic Characterisation of Four Exotic Species for Historic … 125

• The rays, appearing like stips on the included for completeness of the cross section are other indicators of a identification key. species by their width and proportion (Figure 1 - E). On the tangential and radial 3. Results and Discussions surfaces, the height of rays can be measured as different information in From the images produced at various species identification. magnifications, the larger magnification 200x contains more detailed information, but the area included has less anatomical details, while the smaller magnification 40x gives more information about the pores distribution within and between annual rings, but some details, like parenchyma, are not really visible. Therefore 100x was chosen to be representative for the species as the best compromise for the space limit of an article. The reference images for identification purposes of the four investigated species: American mahogany, African mahogany, wenge and eucalypt are presented in Figure 3 and Figure 4 on the transversal, tangential and radial sections.

The macroscopic views of the radial Fig. 1. An example of an exotic diffuse section for these species are contained in porous species, American mahogany Figure 2 and are used as references for the (Swietenia spp. ) - Hoadley, 2000: A - macroscopic characterisation of the species concentric lines of terminal parenchyma; considered in this study. B - vessels with white or gum deposits; For all four species detailed identification C - solitary pores; D - radial multiple keys were thought based on the knowledge pores; E - rays, barely visible to the naked from the reference literature [5], [6], which eye on cross section are available as an electronic catalogue developed within the framework of this • The parenchyma cells, distinguished research project and guiding the user through by a more porous appearance and different sequential steps towards identification, but colour (usually lighter) compared to the here, only the main characteristics are neighbouring wood cells, can confirm, by briefly presented in correlation with the their presence and characteristic arrangement, microscopic images and the macroscopic the affiliation to a certain species. When views. the parenchyma cells appear independent from vessels are called apotracheal (Figure American mahogany ( Swietenia 1 - A) When the parenchyma is associated macrophylla King.) Characterised as an with vessels is called paratracheal, taking exotic diffuse porous species, American certain shapes around the pores, that helps mahogany has a narrow light pinkish- the identification (Figure 4a). greyish sapwood and a yellowish brown Together with the microscopic images of heartwood (Figure 2a). The pores, visible all four species the macroscopic appearance also with the naked eye, appear in on the radial section of the samples was proportion of about 9% with a distribution

126 Bulletin of the Transilvania University of Bra şov • Vol. 3 (52) - 2010 • Series II

a) b)

c) d)

Fig. 2. Macroscopic views of the radial sections of: a) American mahogany; b) African mahogany; c ) wenge; d) eucalypt of 2-7-12/mm 2. Their diameters range and have diameters between 35-145-230 between 100-150-200 µm, are partially µm as it can be seen in Figure 3d. The rays filled with brown deposits, and are either are heterogeneous, 14.8-20.8-28.2%, with solitary or radially grouped (frequently in a frequency of 3-5-9/mm. They can be pairs) (Figure 3a). Rays are heterogeneous uniseriated or 5-7 seriated with 9-19-43 (horizontal and vertical parenchyma cells), cells on the height, meaning about 300- in proportion of 13% and 1 to 4 seriated 520-1100 µm (Figure 3e). Fibers appear in with heights between 300-460-550 µm, proportion of 47.2-57.2-72.4%, have meaning 18-24 cells on the height (Figure lumenii of 4,6-15.5-26.3 µm, cell wall 3b,c). Fibers are present in a proportion of thickness (2 walls) of 3,3-5,2-9,7 µm and app. 74%, have lumenii between 10.8- lengths ranging from 500-1289-2000 µm. 17.6-27.1 µm, wall thickness (2 walls) of African mahogany contains paratracheal 4.2-4.8-6.2 µm and lengths ranging from vasicentric parenchyma, which can be 700 to 1300 µm. American mahogany continuous or, in Figure 3d,e, unilateral. contains continuous stripes of terminal apotracheal parenchyma grouped in 3-4 Wenge ( Milletia laurentii De Wild). As cells (Figure 3a,b). an exotic species with diffuse pores, wenge has narrow sapwood with a light grey African mahogany ( Khaya ivorensis colour and a stripped dark brown to dark- A.Chev.) African mahogany is an exotic violet heartwood (Figure 2c). The pores, species, diffuse porous with a pinkish- visible with the naked eye, are solitary or brown to dark reddish heartwood and in small groups, 1-2-3/mm 2 with diameters narrow sapwood coloured as light greyish varying between 80-235-380 µm and with pink (Figure 2b). The pores, in percentage a proportion of 1.1-6.3-11.5% (Figure 4a). of 10-17.7-29%, are solitary or in pairs, The heterogeneous rays appear 6-7-8/mm rarely grouped in radial rows. They are in various proportions between 17-19- partially filled with dark brown deposits 21.8%, are 1-3-4 seriated and have variable

Gurău, L., et al.: Microscopic Characterisation of Four Exotic Species for Historic … 127

a) d)

b) e)

c) f)

Fig. 3. Micrographs at 100x magnification: a), b), c) American mahogany (Swietenia macrophylla King.); d), e), f) African mahogany (Khaya ivorensis A. Chev.); a), d) transversal sections; b), e) tangential sections; c), f) radial sections heights between 175-210-235 µm (Figure walls). The presence of paratracheal confluent 4b). Fibers are longer than in mahogany, parenchyma is obvious as lighter brown with values ranging between 1540-1760- tissues around the pores in Figure 4a or as 2060 µm. They appear in proportion of lighter strips with stratified regular cells in 35.6-43.3-55.1%, have lumen of 1.3-4.4-7 Figure 4c. µm and thick walls of 4.8-9.7-14.5 µm (2

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Eucalypt (Eucalyptus globulus Labill.) medium, with diameters ranging between Also an exotic diffuse porous species, 80-110-150 µm, visible with the naked eucalypt has a pink-brown to dark reddish- eye. They are numerous, in proportion of pink heartwood, while its sapwood is app. 21%, contain tylosses and appear narrow with a light greyish pink colour solitary or in radial groups (Figure 4d). (Figure 2d). The pores are small to Rays can be homogeneous or heterogeneous,

a) d)

b) e)

c) f)

Fig. 4. Micrographs at 100x magnification: a), b), c) wenge (Milletia laurentii De Wild); d), e), f) eucalypt - Eucalyptus globulus Labill; a), d) transversal sections; b), e) tangential sections; c), f) radial sections

Gur ău, L., et al.: Microscopic Characterisation of Four Exotic Species for Historic … 129

uniseriated, having widths of 8-12-22 µm accordance with the original material. and heights of 90-160-230 µm (9-19-43 Most often, a visual examination of an cells), (Figure 4d,e). Their proportion is investigated sample does not bring enough about 14% and are distributed 11-13- information about the original species, but 15/mm. The fibres are present in this can be definitely resolved by a proportion of app.49%, have lengths of microscopic investigation. 1000-1210-1480 µm, with thick walls 4.2- Species identification can be performed 5.6-7.5 µm (for 2 walls), while the lumenii if the microscopic images are interpreted range between 4.4-6.7-13.2 µm. Eucalypt for their common, but also specific presents paratracheal vasicentric parenchyma features and characteristics by means of in proportion of 16% more visible on identification keys and in comparison with transversal and tangential sections as the reference images. magnification gets higher (Figure 4d,e). This paper referred to four species The results presented above can be used commonly used in historic furniture, for as reference images for species which reference microscopic images were identification, where guiding keys are prepared together with their identification narrowing the search from the most keys: American mahogany ( Swietenia common characteristics (e.g. the species is macrophylla) , African mahogany ( Khaya a hardwood), to a more specific indicator ivorensis ), wenge ( Milletia laurentii ) and (e.g. distribution of pores and growth areas eucalypt ( Eucalyptus globulus). The results can differentiate an exotic species from a can be used in activities of species temperate hardwood). identification in laboratories working in The four species studied in this paper are the field of wood cultural heritage among the 22 wood species important for conservation and more information as an historic furniture, studied as a part of a electronic catalogue referring to 22 wood research project ID_856: Development and species important for historic furniture is implementation of an advanced scientific available for those interested in wood research methodology for sustainable species identification. furniture restoration-conservation and eco- , for which a comprehensive Acknowledgements collection of microscopic images at various magnifications together with their The authors would like to gratefully identification keys have been prepared as acknowledge the support of the National an electronic catalogue. Council of Scientific Research in the Higher by funding the research 4. Conclusions project ID_856 within which this research has been carried out. The conservation of historic furniture has lately become more and more involved References with a scientific interdisciplinary approach. In this sense, knowing the species 1. Andrews, J.: British Antique Furniture . characteristics of a certain historic style London. Antique Collector’s Club, has an important role in the identification 2005. of the respective style. Also, any 2. Cionca, M.: Stiluri şi ornamente la restoration intervention that involves wood mobilier (Furniture Styles and completion or a well justified replacement Ornaments ). Bucure şti. Editura Didactic ă should be very well documented and in şi Pedagogic ă, 1991.

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3. Hoadley, R.B.: Understanding Wood. practice (The Study of Wood. Handbook A Craftsman’s Guide to Wood of Practical Applications ). Bra şov. Technology . Newtown. Taunton Press, Reprografia Universit ăţ ii din Bra şov, 2000. 1979. 4. Ives, E.: A Guide to Wood Microtomy. 6. Wagenführ, R.: Holzatlas . Leipzig. Making Quality Microslides of Wood Fachbuchverlag, 2000. Sections . Suffolk. Edition Ernie Ives, 7. *** Research Project ID_856. Available 2001. at: http://www.artimar.ro/ct/index.htm. 5. Pescarus, P., Cismaru, M.: Studiul Accessed: 15-05-2010. Lemnului. Îndrumar pentru lucr ări