This may be completely unnecessary but I've got some random spools of what I think are silk PLA but I can't remember where I got them and the spools aren't labelled so this is a small patch of squares to print the base in PETG and then the other squares in the mystery material.

My thoery is if they stick then they're PETG but if they slip off they're probably silk PLA.

Probably an easier way to tell but I dunno