Collotype

Prompt

Identify

You see a printed image with smooth tonal transitions, deep shadows, and delicate highlights. Close inspection reveals a [microscopic, worm-like reticulated grain¹] instead of standard printing dots.

Principle

A glass plate is coated with [light-sensitive gelatin] and baked. Exposure hardens the gelatin, making it [absorb greasy ink] in proportion to the light received.

Example

Eadweard Muybridge: Animal Locomotion, 1887.

Try it out

Magnify a high-quality vintage postcard from the early 1900s to look for random, cracked-mud textures instead of organized dots.

Background

Alphonse Poitevin invented the basic process in 1855, but Joseph Albert perfected it in 1868. He replaced a fragile stone base with a glass plate. The process relies on dichromated gelatin². When exposed to light under a negative³, the gelatin hardens. Baking the plate creates microscopic wrinkles in the gelatin. During printing, the plate is dampened. Soft, unexposed areas absorb water and repel greasy ink. Hardened, exposed areas repel water and hold the ink. This allows for incredibly smooth, photographic gradients. Collotype became the premier method for reproducing fine art and high-quality postcards.

Distinction

Unlike halftone printing, which uses a regular grid of distinct dots, collotype uses a random, continuous-tone wrinkle pattern.

Aftermath

It demonstrates how exploiting the physical limits of a chemical binder can create reproductions of unmatched photographic fidelity.

Question