@99p they're a bargain whatever they turn out to be.
Ok triangular / square .... obviously the same in your universe ....no matter. It is unusual for this type but not nec cause for suspicion IMHO.
The crackling is quite fascinating. I've never seen such sparse crackle before. Crackling was popular in Victorian era which is when these would like to belong. Proving that is the next part.
The first thing I'd do it put them under black light. If positive (green glow) thats most likely a good sign.
I am inclined to think Bohemian but others here will know better than I.