Oil as a Woodworking Finish
Oil finishes have been used for centuries to treat and preserve wood. Oil finishes seep into the wood and penetrate the wood’s fibers. Because of this, oil finishes cannot be built up to a thick coat like polyurethane or varnish can. They are probably the easiest finish to apply, however they offer less protection since they are succeptable to wear. Another advantage is that minor repairs can be accomplished by simply wiping on more oil.
When referring to wood finishing, oils are commonly divided into two major types: drying and non-drying oils. The term drying is somewhat of a misnomer, but refers to the hardening or curing aspect of the oil. Non-drying oils should be avoided since they have numerous disadvantages for wood finishing: the finish may remain sticky for a long time, the finish will stain objects in contact with the finish, the finish continues to penetrate the wood (reducing its effectiveness over time), and often bacteria can penetrate the oil and make it emit a rancid smell.
In general, oil finishes create a film that is typically hard, non melting and usually insoluble in organic solvents (varies with the particular oil).