AMBROTYPE process, The

If a very thin under-exposed negative is placed in front of a dark background, the image appears like a positive. This is because the silver reflects some light whilst the areas with no silver at all will appear black. This is the principle behind the Ambrotype process, the pictures being more correctly known as Collodion positives.

Ambrotypes were made from the 1850s and up to the late eighties, the process having been invented by Frederick Scott Archer in collaboration with Peter Fry, a colleague. Ambrotypes were direct positives, made by under-exposing collodion on glass negative, bleaching it, and then placing a black background - usually black velvet, occasionally varnish - behind it. Though Ambrotypes slightly resemble Daguerreotypes, the method of production was very different, and Ambrotypes were much cheaper.

The Ambrotype process was yet another method of reducing the cost of photography. It became popular for a number of reasons:

• less exposure time was needed
• production was cheaper and quicker, as no printing was required
• as the negative could be mounted the other way, by placing the collodion side on top of the backing material, there was no lateral reversal, as there was in most Daguerreotypes.
• unlike Daguerreotypes, they could be viewed from any angle

Ambrotypes became very popular, particularly in America. The process is also called "Melainotype" in the European continent. Another variant of this was the Tintype process.