since I have used it a lot over many years, but primarily for wood (furniture) finishing, allow me to share some shellac tips and trivia.
I prefer to make my own "cuts" which is just lingo for the ratio of solids to solvent and is described in "pounds" with is dry weight per a gallon of solvent.
You buy the solids in various forms (flakes, seeds or buttons are typical) and shades (orange, amber, blond or "super blond" which is what Bullseye/Zinnzer sells as "clear", but it has some straw color).
Solvent should be as close to pure water-free alcohol as you can legally obtain: 99% pure used to be typical, I try to find "wood alcohol" versus ISO-propol but these days (and in California) you take what you can get.
Shellac, even in dry form but especially when prepared in a solution, has a limited "useful life", it will eventually go bad. True even of the cans of Bullseye or the rattlecans, so mark the date you bought it on the can or jar. With experience you can judge the condition by sight and sniff before using and don't use expired shellac on anything "important". I was told rule of thumb is nothing over 6 months old for "quality" projects, but if a year old "it's expired". YMMV.
But removal or "bad shellac" with alcohol is sometimes easily done, depends on the application. Some grades of dry shellac contains a percentage of wax, the most refined grades are "de-waxed".
Brushing: we were taught to use a pure China bristle brush for shellac, nothing else (but I know conservationists who use MUCH pricier brushes, they can afford those) A really good quality China bristle brush costs a bit but the cheapest "chip brushes" are also China bristle and can work ok and be used and tossed, but expect some bristles to pullout. if you spent money on a good brush then clean it after each use with alcohol, then soap and water, rinse very well and form the bristles to air dry. Don't use a wet brush with shellac, it must be dry of water, damp with alcohol is "OK" but it will dilute the solution to some degree.
We were also taught to brush shellac out quickly, in one direction (with the grain if on wood), overlap strokes just enough to coat evenly then DON'T try to coat again until that coat is dry). Don't brush "back-n-forth". If any "sanding" is needed between coats use fine steelwool, but tack cloth that thoroughly to pick up any residue, especially steel particles. if you use synthetic scratchy-pads you won't have steel particles to worry about, but you will have plastic bits.
Shellac is considered a nearly "universal undercoating", nearly compatible with anything except it will not stick to wax! So very versatile as a inter-layer between old and new finishes and can be a barrier, too. Pigmented shellac can seal knots in wood, cover and hide stained surfaces and you can add colorants yourself to created tinted shellac. I like Mixol tints for this, myself, but don't use any solvent-based UTCs with shellac: check the labels!
Much more info than anybody asked for, I know....you're welcome!
