On glow plug airplanes, I use clear tautening and non-tautening butyrate. On diesel airplanes, I use tautening and non-tautening nitrate. I used to be able to tell butyrate from nitrate by smell, but no more. So I have taken to labeling jars using thin line masking tape; XN, TN, Xb and Tb. This has greatly cut down on consigning anonymous jars to the trash.