Abstract
Dried varnish is rich in many ester moieties, which may be broken down into small, soluble compounds by esterase activity or alkaline hydrolysis. Two methods for varnish removal have been developed, including the treatment of either lipase or RbOH / PEG-400 crown ether which allow aged oil varnishes or paint coverings to be removed or thinned. These techniques are designed to proceed in a controlled manner without damaging lower paint or base layers. Unfortunately, lipase did not react with the aged ester groups of dried linseed oil varnish. Surprisingly, the varnish came off in the presence of Tris buffer alone which, in addition, formed reactive metal complexes. A better choice was the use of high Mr alkali ion polyethylene glycol–400 (PEG-400) crown ether type chelates. PEG-400 complexes alkali ions including rubidium and other alkaliions impeding the diffusion of their basic counter ions into lower varnish or paint layers. Possible migration of alkali metal ions into the paint layer during alkaline varnish removal was determined by labelling the cleansing solutions with 86Rb. Fortunately, varnish is degraded on the surface only. Lower paint or varnish layers are not attacked even if chemically similar to the varnish or over painting to be removed as virtually no 86Rb was detected on the paint surface.
Highlights
Varnish is the final, sealing layer of a painting, imparting depth, luminance, gloss or matte while protecting it from mechanical as well as atmospheric influences.Vol 2, Nos. 1-2, 2004Alkali-Ion-Crown Ether in Art and Conservation: The Applied.Bioinorganic Chemistry ApproachThe varnish layer itself is the most exposed layer of a painting and should in cases of age-related discoloration be removable
It could be shown that neither fresh linseed oil nor linseed oil varnish with a lead siccative contain significant amounts of free carboxylic acid or ester groups which can be hydrolysed at 25C
Current reaction mechanism postulates that the drying of linseed oil begins with an autoxidation of the glyceride fatty acids within the oil
Summary
Varnish is the final, sealing layer of a painting, imparting depth, luminance, gloss or matte while protecting it from mechanical as well as atmospheric influences. The discovery of distillation in the late Middle Ages led to the application of turpentine oil and as resin solvents resulting in improved varnishes. The large relative molecular mass solvent PEG-400 was expected to form complexes with alkaline ions as macromolecular crown ethers impeding the diffusion of their basic counter ions into lower varnish or paint layers. These two biochemical approaches employing enzymic and bioinorganic methods in the cleaning of paint surfaces will be comprehensively dealt with
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
