The following is an excerpt of an article by Donald C. Williams
Senior Furniture Conservator, ConservationAnalytical
Laboratory at the Smithsonian Institution
However, the potential difficulty from using oils as polishes or cleaners is enormous. There are two basic types of oils with which we are concerned; drying oils and non-drying oils. The predicament you face is that regardless of which oil you have, there are serious problems. Non-drying oils tend to be the more benign, but there is the issue of an oil remaining liquid on (or in) the surface of any object. Dust and other airborne contaminants readily stick to wet surfaces, especially oils. At least these oils (paraffin, mineral, "lemon oil", which is usually mineral oil with colorants and perfumes added, etc.) don't really undergo chemical reactions or directly damage the furniture.
Drying oils, such as linseed, tung, or walnut oil, are a different matter altogether. These materials solidify, or "dry" through a process of chemical reaction with the air called oxidation. The drying process polymerizes the oil, making it increasingly intractable with time and more difficult to remove with cleaners or solvents. This is fine if oil is employed as the finish, but not good if it is used as a polish. By itself, having a polish which is difficult to remove would be irritating but not insurmountable. Unforunately, this is not the whole story. As drying oils age, they tend to become yellow or brown. Also, drying oils are chromogenic (they become colored) in the presence of acids. In this instance the oil adopts the dark, muddy brown/black opaque appearance so prevalent in antique furniture. Traditionally, cleaning/polishing concoctions were comprised of linseed oil, turpentine, beeswax, and vinegar (acetic acid). This cleaning/polishing method, used widely even in the museum field until recently, was and is a disaster waiting to happen. The results of this approach are readily apparent to even the casual observer; a thick incrustation of chocolate colored goo which is neither hard enough to be durable nor soft enough to wipe off easily. Thus, due to the polymerization of the oil as it dries and the reaction of the oil with acetic acid, the furniture is left with an unsightly coating which is very difficult to remove without damaging the surface of the object.
