Cellulose is a very brittle material, and plasticizing it makes for an inherently unstable material because the plasticizers are all unstable substances which deteriorate or leach out after a number of years. Early lacquers used castor oil or camphor as plasticizers but as time went by the list of materials grew too long to begin to list all the different substances used for this purpose. Some synthetic materials are even used to try and make the films more long lasting. The history of old nitrocellulose film is a good example of the lack of longevity of this kind of material this is why there is a film restoration business. Likewise, the problems of finishes cracking and their poor adhesion on guitars can also be traced to this phenomena.
Many older instruments have almost nothing but the cellulose left on their surfaces.
The film shrinks to about one-third of its original thickness and becomes very brittle, requiring French polishing to improve its appearance and to add some flexibility. Guitarist who love lacquered guitars need to take extra precautions against exposure to extreme cold, otherwise the plasticizers can get brittle and surface shrinkage can cause the finish to crack. Other finishes sometimes used in guitar making are enamel varnish and acrylic enamel finishes. Many varnishes used at the turn of the century were basically very similar to these finishes except that the earlier materials tended to use more natural oils as resins. The enamel material has a special quality as it dries.