How the Alternative Process calculator works

Summary

Calculator for UV-exposed alternative processes: turns process choice, UV source, and negative density into a target exposure time and contrast adjustment.

How it works

Alternative processes are old or unusual photographic techniques (cyanotype, platinum/palladium, Van Dyke brown, salt prints, gum bichromate, and others). Most of them are exposed by ultraviolet (UV) light from the sun or from a UV lightbox. This modal helps you work out exposure for those UV processes from your meter reading and the process you have chosen.

Process

Pick which alternative process you are printing in. Each one has its own UV sensitivity, contrast curve, and typical exposure time. Cyanotype is fast and forgiving. Platinum is slow but contrasty. Each picks up a different recommendation.

UV source

Are you exposing in direct sun, in shade, or under a UV lightbox? Each one has very different intensity. Direct summer sun can finish a cyanotype in five minutes; the same print under a hobby UV lightbox might take twenty.

Negative density

Alt-process negatives are usually printed at 1:1 contact. They need a much denser negative than a standard silver gelatin print, because the UV-sensitive coatings have a long contrast range. The modal lets you tell it whether you are using a normal negative or a digital negative made for the process.

Reading the result

The modal gives you a target exposure time and a recommended contrast adjustment. Test-strip a small area first; alt-process is famously variable and one calculation is a starting point, not a guarantee.