Tintypes Then and Now
I just saw a link go by on facebook to a wonderful set of tintypes produced by a gunner named Ed Drew in Afghanistan. These are available to view here.
These are very evocative tintypes. The soldier mentions the length of time, and the possibility of being called to action, but the side bar doesn’t properly explain why the process is so precious. So here’s some detailed but concise history and science for the interested. You can also consider this class How Photography Works 102 (or Art 150. B&W Photography if you are at UC Santa Cruz).
The length of the process is all in the prep work, not in sitting like we think of really old photography with grim or haunted facial expressions. Tintypes involve preparing a sheet of iron for exposure – a more accurate a.k.a. is ferrotype. These were cheaper and more durable than ambrotypes, which used glass but are otherwise the same technology. Both use a photosensitive colloid emulsion, really a colloid, an evenly dispersed suspension of (in this case) light sensitive crystals in a fluid or gelatin that will “set” on a surface, like the iron or glass, or on paper like modern prints. Because of the gelatin, other chemicals can enter the suspension without disturbing the crystals.
Usually, the crystals are silver bromide, made using silver nitrate, potassium bromide, and potassium iodide, and the emulsion requires working in a darkroom with a red safelight. You can buy the emulsion with modern recipes that include other things in them that greatly improve the process, but doing it retro is pretty fun, and it’s simple with the right materials. There’s a lot of heating and careful stirring involved, though. You slowly precipitate the silver nitrate solution into the liquid gelatin with potassium bromide and potassium iodide in it to produce silver halide grains. The positive silver ions bond with the negative bromine ions and some iodine to form crystals. There’s a lot of by-product with the leftover potassium salts which then need to be leeched or washed out of the emulsion. I’ve heard you can do it by packing the gel into cheesecloth, or use chemicals, but you can also just wash it repeatedly like noodles for a pasta salad. There are also (very important) some free positive silver atoms floating about in this suspension.
When light hits the emulsion, the light photons knock of one of the bromine’s extra electrons, sending it off. Those electrons will attract the free silver and they will start producing clumps in the crystal. Those clumps form the image, but it isn’t visible. These clumps can then be developed through the use of an other chemical (usually iron salts) to become bigger pieces of metallic silver. A chemical used as a fixer (another salt) stops the process, removing excess faint silver halide so it doesn’t convert to much metallic silver. This gets you a nice negative of the image, like standard negative 35mm film we are accustomed too. If you wanted to print it, you’d have to repeat the process with paper. But, if you use a reversal process developer, you can do the opposite, and make a positive image in the emulsion instead. That’s what tintypes and ambrotypes do. Quality is good, so you never need to make a print, vastly speeding up the end process and providing quick memento images of quality for tourists and fair-goers worldwide! (That was the primary market!)
Prep work like this allows for short exposure times, but the produced negative is soft and underexposed. The iron is given a black layer with paint or enamel before the photosensitive emulsion is applied to darken the picture, making the soft positive look like a vibrant print. So what you are looking at is not a laboriously printed piece of paper, but a laboriously prepared slide of metal.
Developed in the 1850’s, this technology was both state-of-the-art and well-practiced enough by the time of the Civil War. The ability to take quicker photographs was a factor in the ability to take journalistic and documentary photos during the Civil War: a photographer could set up shop and prep a series of iron slides and take them out to the action. But those photographers were civvies; if our gunner was called out at any time during the prep process, he’d loose those precious metal slides.