Gelatin was used for decades after its discovery as an emulsion base before scientists discovered what made it tick. Most obvious and easy to understand is its action as a protective colloid – the gelatin keeps the silver grains suspended and helps them grow to controlled sizes. Gelatin melts and sets again and again with little change in character. It dries hard. But gelatin did something else. It greatly increased the sensitivity of the emulsion.
Modern photographic gelatin is a highly purified and standardized product. The early gelatins used for photography were anything but. There were dozens of brands in use, each with its own characteristics. Jelly strength (hardness) was easy to measure, but it was harder to quantify the sensitizing ability of a particular brand of gelatin or even between different lots of the same brand. Stories grew of secret herds of cattle grazing on secret fields of secret plants that produced the ‘fastest’ gelatin. When it was noticed that gelatin made from cows that had grazed on mustard fields was especially effective, it wasn’t long before it was discovered that sulfur compounds in gelatin increase the speed of an emulsion.
This was a great discovery for photographic science, but today it causes photo-technique detectives no end to grief. It’s hard to know the characteristics of ‘Nelson’s No 1’ gelatin or ‘Heinrich’s’. For us, it’s as much trial and error as it was our photographic predecessors. A hundred years ago, every emulsion company had a testing protocol for each batch of gelatin that hit the loading dock. For both the purpose of emulsion making for personal art’s sake and for the history of it all, understanding gelatin is as important today as it was in 1871. - Denise Ross