Spectral imaging of Dutch gilt leather for improved conservation strategies

Gilt leather was one of the most fashionable and costly types of wall-hangings in the Western world in the 16th to 18th centuries.It has a gold appearance which is the result of a silver leaf coated with an orange-brown varnish.It is a layered composite of organic and inorganic materials, including leather, animal glue, silver metal-leaf, varnish, and oil paint.Ageing processes are complex due to many interactions between these different materials, which makes conservation a real challenge.Furthermore, the common conservation treatments practiced in the past resulted in negative side-effects over-time such as gloss and colour change (darkening) and stiffening of the support.Hyperspectral imaging is a proven non-destructive method that has been used in conservation for more than two decades, mostly for the examination of paintings and manuscripts.With its use, it is possible to reveal features and their locations invisible to the naked eye, such as thin varnish layers, paint and overpaints or underdrawings.In this study, a collection of gilt leather objects was studied at SRAL.Data were analysed using a software analysis platform (TIPP), developed at AeroNDT.The results show maps of quantitative pigment concentration and areas with possible chemical degradation or silver tarnishing.