A photographic process in which the negative image is produced on a thin, coated plate of iron (there is actually no tin involved). Tintypes first appeared in 1854 and enjoyed their widest use in the 1860s and 1870s. Video here.

Edwin Chamberlain of Company G, 11th New Hampshire Infantry, in sergeant’s uniform with guitar. Tintype. 1861-65. Library of Congress, Washington, D. C.