Buried in the parts list of a wartime Signal Corps darkroom manual is a single item that hides an entire lost craft:

12 Plates PH-152 or PH-152-A, ferrotype.

This was the standard field-darkroom kit issued to Army photographers in 1943, printed by the War Department to teach soldiers how to develop, fix, and finish photographic prints under combat conditions. Twelve ferrotype plates traveled with every kit. Why twelve? Because in 1943, if you wanted a glossy photograph, you had to make it glossy — the paper alone would not do it.

A ferrotype plate was a sheet of chromium-plated steel (or japanned tin) polished to a mirror finish. After a print was washed, the photographer would squeegee it face-down onto the plate and let it dry. As the emulsion contracted against the polished surface, it took on a perfect physical replica of that mirror. When the print popped free — often with an audible tick — it had a shine no modern inkjet can match. The gloss you were looking at was not paint or coating. It was the reflection of the steel, transferred into the gelatin itself.

The technique demanded near-religious cleanliness. A single fingerprint or fleck of dust on the plate would be reproduced, in glossy relief, on every print pressed against it. Photographers waxed their plates with beeswax or a proprietary "ferrotype solution," buffed them to a haze, and stored them wrapped like fine silverware. When a plate got scratched, it was ruined — hence the Army packing a dozen spares.

What killed the ferrotype plate?

• Resin-coated (RC) paper, introduced by Kodak in the late 1960s, baked the glossy surface into the paper itself. No pressing required.
• Ilfospeed and similar products in the 1970s made glossy prints available to any home darkroom hobbyist without the ritual.
• The rise of digital printing finished off any lingering use.

By 1985, ferrotype plates had vanished from photo supply catalogs. Today, a photographer under fifty has likely never seen one. Yet those glossy black-and-white portraits you find in grandparents' albums — the ones with the impossibly deep blacks and a shine like wet ink — almost all owe their look to a piece of polished steel that the Army thought important enough to issue in dozens.

There is a modern echo: fine-art printers using platinum-palladium or silver gelatin still occasionally hunt down old ferrotype plates on eBay because nothing since has produced quite the same optical effect. The gloss of a 1943 print is not a coating you can buy. It is a fossil of a mirror.