preservation of tintypes

Grant Romer (romer@ee.rochester.edu)
Mon, 1 Apr 96 09:29:25 EST

Risa,
There are two types of oxidation that can occur with tintypes. One is the
formation of iron oxide (rust) due to moisture getting to the iron
support, usually through small scratches or holes. The corrosion can
extend under the emulsion layer and eventually cause sections of the
emulsion to flake off. There is no good cure for this. To halt this type of
deterioration, the image should be sealed with a cover glass and a spacer
(to keep the cover glass from touching the image). Keep the image is a
warm dry place. Oxidation of iron can not be reversed.

The other type of oxidation that can occur with tintypes is the oxidation
of the silver imaging substance. If the tintype was not varnished after
the image was made, the silver which sits on top of the collodion binder,
can react with oxidants in the air, forming silver oxide or silver sulfide.
Non-varnished tintypes are found only from the very earliest years of
production when they were still being placed in cases like daguerreotypes
or ambrotypes. If the original exposure was too dark (not enough
exposure) it was sometimes left unvarnished, as the varnishing always
made the image darker.

This second form of oxidation appears as colorful bands or rings of
tarnish on the surface of the plate. It is never mistaken for oxidation of
the iron support.

Hope this helps. Further information is available from me at any time.

Roger Watson
Conservation Laboratory
George Eastman House
900 East Ave.
Rochester, NY 14607
(716) 271-3361 ext. 323