BEHAVIOUR OF ANIMAL-ORIGIN GELATINS TO ARTIFICIAL AGEING IN THE PROCESS OF RESTORING GILDED WOOD

Abstract

Animal-origin glues are adhesives made by boiling animal tissues for a long time, and from the chemical point of view they are gelatinous and albuminoid protein substances bearing different names. The most frequently used are gelatins. They are extracted from raw animal hide residues, from cartilages, tendons, and from the gelatinous matter extracted from bones, on which the name and quality of gelatin depends. The gelatin extracted from unhaired hide waste/pelt waste resulting from unhairing bovine hide from tanneries was used in this article to study the behaviour to accelerated ageing of two types of gelatins used for gilding some wood samples with gold leaf. In this paper we aimed to find the damaging effects of heat and relative humidity on the gelatines (extracted from bovine hide and rabbit skin) based adhesives used for wood gilding. Therefore, a gold leaf was applied to a fir wood (pine tree) conditioned for ten years using commercial gelatin extracted from rabbit skin as well as gelatin extracted from bovine hide by-products. The gilding technique followed the traditional recipe in which adhesive, multiple layers of plaster, bolus were employed in order to fix the gold leaf. The gilded wood prepared as such was artificially aged in a special Binder-type aging chamber at 60? for 7 days, followed by conditioning in an incubator at 70% R.H., at 25? for 2 days, in nine cycles. The physical�chemical changes of gelatin-based adhesives resulting from these conditions, as well as stratigraphic and microstructural characteristics of gilding layers were analyzed by applying optical microscopy, colorimetric measurements and infrared spectroscopy with attenuated total reflection (FTIR-ATR). The obtained results showed that both gelatins have very good adhesive and structural properties and could be successfully used in the field of conservation and restoration.