The case of Realgar and Orpiment degradation due to photo-oxidation: The optimum (or at most the best) lighting system applied to cultural heritage A. Macchia*, G. Roscioli*, L. Campanella**, D. Gazzoli***, A. Maras** *Italian Association of Conservation Scientists **Center of Sciences Applied to the Protection of Environment and Cultural Heritage,– University La Sapienza of Rome, ***Department of Chemistry‐ University La Sapienza of Rome

safe conservation of the exposed objects Museum: For exhibition of optimal vision offered to visitors for their cultural heritage satisfactions and enjoyment

Conservation aspects: it’s necessary to consider both the possible deterioration due to the radiation falling on the object and other aspects such as micro‐climate conditions, frequency of visitors.

The aim of this project is to determine the extent at which the range of the available systems for illuminating works of art can be characterized, implemented ,improved or modified, even by standardization process in presence of the same materials of cultural heritage to be protected Project work is being carried out: 1. by investigating light‐induced structural changes in realgar and orpiment minerals 2. By examining existing light sources, their lighting “quality”, to develop a new system, based on LED technology, able to combine visual valorization with protection of Cultural Heritage

in cooperation with Realgar and orpiment are of archaeological and medieval interest because of their use as pigments both in painting as in cosmetics since prehistoric time

Realgar is a red‐orange natural (α‐As4S4 | β‐As4S4) and synthetic (χ‐As4S4 or As4S4 [II]) mineral

Orpiment, As2S3, is an orange to yellow monoclinic arsenic sulfide mineral Light‐induced degradation: of realgar to pararealgar by visible light (500‐ of orpiment to arsenolite

670 nm) causes an increase of As4S4 AS2S3 + 4.5O2Æ As2O3 +3so2 intermolecular distances and the production of

As4S5 molecules according to Bindi et al (2003) [2] who hypothesized this reaction: Arsenolite As2O3(pink or yellow hue) 5 As4S4 (red orange) +3 O2 → 4As4S5 +2As2O3

Realgar was used alone or mixed with a binder: Pararealgar As4S4 (yellow) Lin Oil, gum arabic, egg The experimental results suggest the following cyclic process Lamps used in the study : OSRAM Alo 75 W ; Philips MyAmbiance Spot a LED 16 W (75 W); Osram halostar 50W; Philips masterline ES 45W; Osram decostar 35W The light‐induced alteration Orpimen photoxidation after 9 hours (h), 36 h, 168 h, 338 h exposure to light (alo 75w): As‐As stretches shift from 181‐188 to 228‐232 cm‐1 progressively with the exposure time

Realgar photoxidation: 1. in N2 environment no degradation after 2 week exposure; 2. in air enviroment after 9 h, by the destruction of As‐As bond(s)in realgar molecule pararealgar and arsenolite are produced with kinetics that we studied;Raman spectrum results to be unchanged In the range treatment 1‐2 week; the binders don’t influence neither reduce the realgar degradation

LED 11 W (= alo 75W): The degradation signal is present starting from our test at 26h

Others lamps (36 h): In all, degradation can be observed. Only in the case of 50 w alogen osram as lighting source the realgar is present with pararealgar and arsenolite