Very elucidating! And instructive. The chemistry and physics behind finishes, in particular the ones dating back centuries, even millenia is fascinating and a necessary study especially for restoration and conservation. Shellac (yes ,a deposit from a beetle) dries and does not polymerize, like alkyd resin finishes ( varnish). A shellac finish can, therefore, be amalgamated using alcohol ,or a similar solvent, some being water soluable, that will disconnect its molecules and allow it to be softened and reworked on a surface without removing it altogether, allowing it to be conserved and restored, retaining its color ,acquired over time, and traces of its crackled surface to be retained as evidence of its antiquity. No such luck with old polymerizing (varnish) finishes, where the surface must be slowly and gently abraded to the point where the top obscured layer is removed and the remaining surface polished back to clarity. Both approaches are time consuming and require a great deal of patience and care. The latter being agonizingly slow, produces a lot of toxic dust and no small amount of joint wear. Wear a mask, use fine grades of sandpaper to start with and be prepared for the long haul. Remember, whatever scratches you put in you will have to polish out. old well worn sandpaper is best.
A word about the light fastness of alcohol and water vehicle stains. I was referring to aniline powders or concentrates dissolved in water or alcohol., which can produce nice fast drying and penetrating stains but are susceptible to UV. I have not tested the light fastness of commercially available water based stains like Minwax brand but I believe them to be, thanks to modern chemistry, more durable and light fast as demonstrated by danielesje.
Stay away from solvent vehicle finishing products as much as practicable. In nearly every contemporary case a more environmentally and non poisonous water based substitute is readily available, easier and safer to use and give very satisfying results. Thanks again to danielesje for his very useful and helpful information on this topic regarding model building.
I am happy to receive any correction to, or informed analysis of, my comments . Beyond personal experience I am no authority.
Pete Gutterman