the carbro process

at the Getty Museum

at the Getty Museum

On Saturday, I went on my very first trip to the Getty Museum. While I was there, I happened to chance upon the photo gallery of Paul Overbridge, and to my surprise, there was something to be learned about science there- the carbro process.

The carbro process is the combining of carbon-based pigments and silver bromide prints (hence, the word car-bro) to create a single color print. In order for this process to work, a colloid substance, such as gelatin or gum arabic, must be combined with any one of several chromium salts and then be exposed to light. Afterwards, the salt breaks down, giving off nascent oxygen, which then leads to the colloid becoming more or less insoluble depending on how much light it receives.

During the carbro process, the carbon pigment is placed into contact with the silver bromide print while still wet. Next, the colloid becomes even more insoluble through the chemical reaction as it comes in contact with the silver of the bromide print. Finally, the soluble portions of the gelatin wash off and leave behind the insoluble portions which with their pigment stick to the paper, and thus create carbon print.

The process may sound extremely overwhelming, time-consuming, and even expensive, but the difficulties are often overlooked for the carbro process’ ability to render beautiful, long-lasting color prints.

In fact, here are some of the carbon prints I saw at the museum:

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