"Conservation Treatments of Damaged Photographs" Cased photographs: Daguerreotype, Ambrotype, Tintype, Photographic prints: Salted Paper Prints, Albumen POP, Glossy Collodion POP, Matte Collodion POP, Gelatin Silver POP, Gelatin Silver DOP, Platinum Print, Photomechanical prints: Letterpress Halftone, Collotype, Photogravure ... etc.
Abrasion due to storage with other items causes pieces of the emulsion (image) to flake off.
Humidity in the air then leads to rust where the iron plate is exposed. As the tintype ages, more rust appears and the flaking will continue, eventually destroying the picture.
The collodion surface of tintypes often shows fine crazing or cracking, which distinguishes them from Ambrotypes. May show traces of rust, the result of bends and deep scratche
Variation on the Ambrotype process, but produced on iron sheet (not tin) instead of glassPlate coated with collodion and sensitized just before use;
Became instantly popular, particularly in the United States; also widely used by street photographers in Great Britain.
Cheap to produce, a typical price for a tintype was 6d -1 shilling
More robust than ambrotypes it could be carried about, sent in the post, or mounted in an album.
The material could easily be cut up and therefore fitted into lockets, brooches, etc.
The smallest were "Little Gem" tintypes, about the size of a postage-stamp, made simultaneously on a single plate in a camera with 12 or 16 lenses.
Some tintypes are very dark overall while other specimens have surprisingly good contrast with an almost white background...