Originally posted by melogic
<br />I was wondering the same thing that Tom is saying, "How long will it last?" I would have thought shellac would last a long time, but I don't know a lot about the durability of the finishes.
In the responses to your question, Mark, there is about 3% valid data and 97% supposition. A properly applied finish consisting of boiled linseed oil (BLO), shellac flakes or buttons and denatured alcohol is a very durable finish, once it has cured. The trick is the curing time. If you are using the home-made shellac as your only finish, the items should ideally not be handled for a week...maybe two. The upside is that the shellac will continue to cure for many months, possibly years, adding to it's durability over time.
Many woodworkers complain about the lack of durability of a friction finish, but the facts do not support their conclusions. Most, if not all, of the commercially manufactured shellac-based friction finishes are highly contaminated mixtures which include water, waxes and other oils which are used to extend the shelf life of the shellac (usually 6-12 months when mixed with denatured alcohol only). These contaminants compromise both the structural integrity of the friction polish and its durability. These additives also allow the manufacturers to emulsify to mixture to some degree. Without these contaminants, shellac forms a water resistant finish that is also largely impervious to alcohol and body acids.
The addition of BLO to the shellac/alcohol mixture adds yet another degree of hardness. BLO is raw linseed oil which has had heavy metals added to speed up the drying time and to add to durability of the dried finish. BLO, while not truly boiled, is often polymerized by heating the raw linseed oil to approximately 300-degrees fahrenheit (in the absence of oxygen, it will not boil at that temperature) where the small molecules combine to yield larger molecules of the original, only lined up to form a tight bond. It is this polymerization that adds hardness and durability.
All of this is not to say that shellac-based friction polish is better or worse than the plastics (CA, many lacquers, polyurethane). Heck, you can preserve just about anything in a shiny display by encapsulating it in a thick coat of plastic and polishing it. I've seen rattlesnake heads, tarantulas and even human body parts preserved this way.
The real choice comes down to how you want your work displayed and what efforts you are willing to take to get that result.
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