Tintype (ferrotype)

☠Level D: studied, never performed

A tintype is a wet-plate collodion plate on a different support, and it inherits that process’s classification whole. No procedure appears here.

There is no tin in it. The name is a nickname the trade kept, and the accurate one — ferrotype — says what the support is. It works exactly as an ambrotype does against its backing, except that the dark ground is the support rather than something added behind it.

The chemistry

The wet plate’s, unchanged: soluble halides dissolved in collodion, the silver halide formed inside the film in the silver bath, and a physically developed image plated onto the exposed specks by iron(II) reducing the free silver the plate is still wet with.

The one setting that differs from a negative is the same one the ambrotype uses. Towler’s developer for ambrotypes and melainotypes carries more iron and more acid than his negative developer, because the plate is being exposed and developed to a deliberately weak image; and Towler’s own summary of the balance holds — diminishing the iron and increasing the acid “are correlative expressions”. Modern practice dilutes a concentrated ferrous sulfate developer 1+3 for tintypes and ambrotypes, developed for twenty to thirty seconds, against 1+5 and two minutes for glass negatives after three stops more exposure.

⚗Why moving the black behind the film into the film's support changes everything commercial about it

Chemically, nothing. Optically, nothing. What changes is the object.

A glass plate needs a separate black backing, a case, and care in the post. An iron plate is its own black backing, does not break, weighs little and is flat enough to put in an envelope. That is the whole of the tintype’s commercial advantage, and it is why the process outlived the ones it imitated by decades — the clearest evidence in this atlas that what spread a process was cost and durability in the post rather than image quality.

Historical workflow

The wet plate’s, on a japanned iron sheet, run short and varnished. The fixing choice is the collodion positive’s, and Hardwich’s argument for cyanide applies here as it does to the ambrotype: hyposulphite contains sulfur and is somewhat unstable, so the image is liable to be superficially darkened, while cyanide always produces a whiter picture.

The image

A pale, scattering silver deposit against a black lacquered ground, often hand-coloured, and read as a positive for exactly the reason the ambrotype is: against black, a scattering deposit is a highlight and the ground is a shadow.

It is a unique image with no negative behind it, like every collodion positive — which puts it in the same commercial category as the daguerreotype at a fraction of the cost.

And it is laterally reversed, for the same reason every direct process is: the surface that faced the lens is the surface you look at.

Identification is trivial and worth stating. The support settles it at once: iron under a magnet, and no glass to look through. That is the shortest confirming test in this atlas.

Permanence

The usual damage is mechanical rather than chemical, because the support rusts and bends where glass would break. A bent tintype has a cracked varnish and a lifted collodion film along the crease; a rusting one is losing its ground from underneath the picture.

That inverts the ambrotype’s failure without changing its character. Both objects fail at the interface between a fragile film and a ground that is not part of it, and in both cases the image silver may be in good condition while the thing that makes it readable is not.

The collodion binder’s own long-term behaviour is the wet plate’s question and the course does not answer it here.

Hazards

The wet plate’s, in full — diethyl ether, nitrocellulose, cadmium bromide in the salting mixture, silver nitrate at bath strength, and potassium cyanide where the period fixing is followed — and this entry does not restate them.

Two hazards belong to the support. A japanned iron sheet is cut, so a cut edge is a real injury risk in a process that otherwise has none; and the lacquer’s composition is not something this course has established, so a flaking plate is shedding an unidentified material and should be handled as an unknown.

Why we study it and do not reproduce it

Because it is the cheapest photograph the nineteenth century made, and the clearest evidence that the market chose on cost and postability rather than on quality. Set it against the daguerreotype — the best pictures of the century, unique, expensive, cased — and against the salted paper print — the worst pictures, and reproducible. The tintype is a third answer: worst pictures, unique, and so cheap it did not matter.

Because identification by support is a skill worth having, and this is the process where it is easiest: a magnet settles what no amount of looking at the image will.

And because it completes a triple. Three objects — ambrotype, tintype and wet-plate negative — made from one chemistry, distinguished only by what is behind the film and whether anybody printed from it. Understanding that is worth more than the three entries separately, and it is the reason Part XXVI treats the collodion family in a single lesson.