These tintype photographs, actually on thin pieces of iron, were incredibly popular in the 1800's. Their ease and mobility made it a great solution for carrying personal photographs, particularly for soldiers.
The interesting texture, color and style was used long after other photographic options were available, a lot like the polaroid is continued to be used by some today. The small ones were placed in decorative paper sleeves. You can still find them that way. I liked this small, postage stamp size group of loose portraits I bought on Ebay last year.
In researching tintypes, I found a photographer, Robyn Hasty, who works in this beautiful format now. She teaches classes and shoots tintype personal portraits. Prices vary regarding size and location.
They are simply beautiful.