Varnishing works of art is an old practice that could be dated from the first centuries, even if it is complex to find precise traces of this practice in the field of paper artworks. In literature, it is only from the multiplication of manuals and the development of the general interest in science, typical of the XVIIIth century, that we see varnish recipes appear. Throughout several periods, we will see the use of oil-based varnish ("fat varnishes") or alcohol/essence-based varnishes ("thin varnishes"). The latter is more often used on graphic documents. 
Thanks to these recipes, we can understand the varnish chemical composition, made of various resins of natural or synthetic origin.

​

The varnish plays two essential roles : protection and aesthetic. These qualities could be affected through time : from the materials ageing and subsequent degradations, to occasional interventions of a conservator. All of the degradation phenomenons and interactions between the support and the varnish can be responsable, on a long-term basis, to two different type of alterations : 

• The loss of mechanical resistance for both paper and varnish (like oxidization and hydrolysis)

• The loss of a clear lecture of the artwork produced by chromatic changes during the ageing and bad conditions of storage and preservation

In view of protecting the document and preserve its authenticity, we could consider the option of preserving the varnish or proceed to its removal.

Several varnish removal solutions are possible for the conservator, be it "dry" methods (with scalpel and ultrasound systems) or solvent based. The latter can be used directly (like solvent vapours, cotton swab, blotters, spraying and immersion) or inderectly (like compress and gels).

A further comparative study was then made, considering two principal questions :
- Which method is the most appropriate for varnish removal ? Are there methods less invasive than others to choose a level of intervention ?
- Which effects can produce these methods on media, in particular sensitive media ?

Varnished paper and the methods of removal is a complex but very interesting subject. This study provides just a few steps in the understanding of the varnish removal issue in paper-based artworks.