What are they?

I own about 20 4x4 glass-plate negatives from around 1890-ish. I think they're from the Portland, Oregon area, which is where I was living when I obtained them.

I am printing one of them for the alt. print exchange, and some questions popped into my mind while printing them.

How do I attribute them? Do I mention the era they're from? Do I mention they're glass-plate negatives? Do I just print and present them and not say anything? Clearly they're not my images, but now I own the negatives.

Just some thoughts...this is the first time I've run into this dillemma.