By the late 1840s, the techniques that would evolve into the Kallitype / Van Dyke, utilizing the knowledge of Sir John Herschel’s 1842 inventions of the Argentotype, Chrysotype, and Cyanotype processes, had chemically evolved into popular printmaking options for photographic image makers. Although Herschel had accurately described how the Kallitype process would work, it was not patented, and named, until 1889 by Dr. W. W. J. Nichol.

In Van Dyke, ferric ammonium citrate is the active UV light-sensitive component in the sensitizer, whereas in the Kallitype, ferric oxalate performs that role, as it does in platinum and palladium printing. The Kallitype sensitizer of ferric oxalate and silver nitrate is brush coated on a rag paper, exposed to UV light, where the ferric oxalate is changed to the ferrous state, reducing the silver nitrate to the metallic silver. When developed, the ferrous oxalate is dissipated and metallic silver is left forming the image. Print contrast can be controlled by a combination of sun and shade exposure or chemical adaptation of the sensitizer.

The exposed paper is then developed in a choice of several developers, i.e., sodium acetate, that allow for a variety of color interpretations. The print is then water cleared, toned in one of many toner options, fixed with a simple sodium thiosulfate bath, and washed. The Kallitype is a close cousin to platinum / palladium in its reliance on ferric oxalate and a metallic salt to make an image. Many artists consider the Kallitype to be the equal of platinum  / palladium and there are some knowledgeable folk who still have difficulty distinguishing between the two when the color and image tonality are made to look alike.

The Van Dyke, like the cyanotype, produces an image due to the reaction of ferric (iron) salt conversion to a ferrous state during exposure to UV light. The process depends upon a sensitizer combination of (A) ferric ammonium citrate, (B) tartaric acid, and (C) silver nitrate. A fine piece of paper is brush or rod coated with this sensitizer, dried, placed in a contact- printing frame with a negative, and exposed to UV light. Following exposure, the print is “developed” in water and then briefly fixed in a dilute sodium thiosulfate solution and subsequently washed for permanence.