Most of the old publicity photos were shot in black and white on negative film. Prints were made from the original negative. This is all pretty basic, but a copy of a positive and negative of a Thelma Todd picture turned up, so I thought I'd put them on the blog.
Here we have a positive of Thelma Todd:
This looks like sheet film to me. Most of the old publicity photos used to be shot with large format cameras, which usually used sheet film.