###### Abstract  
In this work, we studied the manufacturing processes and the conservation state of gilt and painted leather fragments from Palazzo Chigi in Ariccia (Italy) by using different analytical techniques. Leather fragments present a silver leaf superimposed onto leather support. A gold varnish and different painted layers decorate it all. A top-down analytical approach was used to investigate this complex multilayer structure, which adopted techniques with different sampling depths. Organic and inorganic constitutive materials together with related degradation products were studied by time of flight secondary ion mass spectrometry (ToF-SIMS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and macro X-ray fluorescence (MA-XRF). The findings have revealed the presence of different elements and species as calcium and iron in the leather support, which was attributed to the un-hairing process in the leather tanning. Regarding what concerns the silver leaf, where the varnish cracked, silver chlorides, oxides, and sulfides were detected as degradation products of the silver leaf. Proteinaceous compounds were also identified where the silver leaf is unprotected by the varnish. These ion signals reveal a potential use of animal glue on both sides of the silver leaf to promote durable adhesion. In the gold varnish, the surface analysis revealed organic compounds such as resins and oils. In particular, the copresence of linoleic, arachidonic, and lignoercic acid ion signals in the yellow area suggests the use of aloe as a colorant. Lead ions in the same area were detected and attributed to the use of lead as sicactive. Blue areas were obtained by using indigo and lead white in addition to an oil binder. This is confirmed by the detection of indigotin, fatty acid, and lead soap ion signals. A copper-based pigment was used to depict the green areas and copper oxalates were identified as its degradation products. Lastly, no significant information about the red colorant was obtained. Colophony is present as a component of the final varnish. leather; MA-XRF; ATR-FTIR; ToF-SIMS; manufacturing process; degradation products +
Footnote †: journal: Applied  
The manufacture of gilt leather begun in North Africa (Ghadames, Libya) and was introduced in Spain during the early Middle Ages. Later, it spreads through Spain toward the rest of Europe [2]. The production of gilt leather consists of a very laborious process. The first step is making the silver leaf adhere to the leather support using animal glue and, subsequently, apply a yellow oil-resin varnish. Recipes stated that the oil-resin varnish forming the golden-like surface on the silver leaf generally consisted of heat-bodied linseed oil with lead components (pigments such as massicot or minium can be used). In addition, resins (such as sandarac, colophony, etc. ), fossils (e.g., amber), and organic colorants (such as aloe, asphalt, saffron, dragon blood, etc.) were added [1; 3]. Decorative motifs were commonly stamped with woodblocks or by techniques of surface modification such as embossing [4; 5]. The last step consisted of applying oil paints and glazes for decorations. Heat-bodied oils or a mixture of oils and resins were used as binding media [1]. The complex overlapping of inorganic and organic materials makes the conservation of this type of artifact very difficult. Among the others, one of the main problems related to the conservation of leather refers to the decorative surface layers. In particular, special attention is dedicated to the tarnishing of the silver leaf, which leads to aesthetic damage of the leather artifacts. Generally, in this type of material, silver tarnishing is promoted by a large variety of factors, such as the natural aging and degradation of the overlapped oil-resin varnish protecting layers that may embrittle generating micro-cracking [3]. In this way, the exposed silver leaf surface can be subjected to degradation phenomena.