A hundred years ago, many portraits were taken on tintype, also called ferrotype.
1 a positive photograph taken directly on a thin plate of black-enameled iron coated with a sensitized emulsion; tintype
2 the process of making such photographs
3typed#, 3typ#ing to give a glossy finish to (a photographic print) by squeezing into contact with a highly polished surface, usually chromium-plated steel, stainless steel, or plastic

The exposure time had to be rather long, minutes, not fractions of a second. Interestingly, the result
was a positive image. Sad thing was that they slowly turned all black. I had one of my grandmother,
which when about eighty years old was almost all black.

There was an emphatic way of saying "No!" --- Not on your tintype!" I have been unable to
fiture out how it came to be used. Word-Detective's parents in their phrase dictionary said
they were unable to find its origin. Let's have some speculation on it.