thanks everyone for the informations...

I made a very small batch this evening (50 ml) using separate solutions and adding denaturate alcohol to the gelatin/potassium bromide solution. Unfortunately that wasn't a good idea: while drying on the paper, the emulsion darkened and printed deep brown. Even a second unexposed sheet turned brown when placed in the developer. My fault - I add plenty of denaturated alcohol at home and wanted to try that. I use the same alcohol for a POP emulsion based on chloride salts and got no problem there.

Tomorrow I'll buy some pure ethyl alcohol. I never heard of thymol, perhaps is popular in the US. I made some research and in Italy is used mainly to fight a kind of parasite in bee colonies. Dunno where to find it.