Thank you all so much for your replies and your research. Well, you guessed it, it is about veganism and my client knows what shellac is and I didn’t use hide glue or fish glue in his guitar (or bone).
He does want a shiny finish (as in guitar shiny). So I guess the best option is nitrocellulose laquer. Urushi would be great but a bit too pricey for this project.
Actually I left out an important information—mostly because I really wanted to know about non shellac possible spirit varnishes—The guitar has a few coats of tru oil (gives it a beautiful satin finish). It was finished that way first then my client decided he would prefer shiny.
The mixture of sandarac and other resins I tried was based on the Watin spirit varnish that I tried to adapt. So really from the tests I made it seems few things stick to anything like shellac does.
Here’s what it looks like now (the clear pickguard is temporary). Shiny would definitely look great on that rosewood.
I am looking for a spirit varnish recipe that does not contain shellac. I am a guitar maker. I usually French polish with a shellac based varnish that also contains other resins. For this instrument, however, I can’t use shellac due to the believes of my client (please don’t make this the focus of the conversation).
I tried modifying a sandarac based recipe, but the varnish was easily scraped off.
I also tried sandarac turpentine and elemi (in alcohol), with the same results.