Definition of "tintype"

She was so mad she wouldn't speak to me for quite a spell, but at last I coaxed her into going up to Miss Emmeline's room and fetching down a tintype of the missing Deacon man.

1913, Joseph C[rosby] Lincoln, chapter VI, in Mr. Pratt’s Patients, New York, N.Y., London: D[aniel] Appleton and Company

There were photographs everywhere: photographs framed and unframed; photographs large and photographs small, the fresh and the faded; tintypes, kodaks, “full lengths,” “cabinets,” groups—every type of photograph; […]

1913, Booth Tarkington, The Flirt, Garden City, N.Y.: Doubleday, Page & Company, page 70

They'll show you tintypes of the kids more often than not, hell, they love em chavalitos.

2006, Thomas Pynchon, “Against the Day”, in Against the Day, New York, N.Y.: Penguin Press, page 885