Workshop: Gum bichromate

TOOLS

Photoshop

A photograph with strong contrast

Permajet Digital Transfer Film 

Seawhite of Brighton A4 Watercolour Paper

Artist's Loft Watercolour ink

Gum Arabic 

Potassium dichromate 

This workshop is in two parts: a digital part and an analogue part.

I grabbed an old image taken with my old faithful iPhone 5 and opened it in Photoshop and converted it to black and white.

The conversion to black and white can also be done via the Black and white option on the adjustment panel.

The curves are adjusted to achieve the desired effect.

On the adjustment panel, select Invert 

The image is then saved as a .PSD and printed on Permajet Digital Transfer Film in an Epson Ultrachrome K3 printer.

That's the end of the first stage. 

Warning: Given the toxic nature of the potassium dichromate, gloves should be worn at all times and, if available, goggles. Any chemicals that are accidently splashed onto the skin should be immediately washed under cold running water. Any chemicals that are splashed into the eyes should be treated with the eye-wash solution and medical treatment sought. I also recommend wearing old clothes and old footwear, in case of accidental spillages.

A solution of 5 ml of gum Arabic was mixed with a pea-sized amount of Artist’s Loft Crimson Red water colour paint. When thoroughly combined, 100 ml of potassium dichromate was added and mixed together.

The mixture was quickly painted on to the A4 Watercolour Paper with a synthetic brush, using north to south and east to west motions, ensuring that the paper was not sodden and there were no visible brush strokes. The paper is handmade and has a lovely thick texture to it, which means that when wet, it won't disintergrate quickly. The paper was then left to dry. 

The digital negative was placed on top of the treated paper and secured under the glass of a clip picture frame. The print was placed in a graphoscreen for 15 minutes. After being removed from the dryer, the print was gently washed in cold water to remove any remnants of unexposed dichromate and any unhardened gum which would then reveal the final image. The print was allowed to dry in a drying rack.

The print has an ethereal, diaphanous quality to it, as though it were a pastoral scene being viewed on a misty morning or through a window covered by layers of gauzy curtains. The strongest parts of the print are on the right-hand side, where the editing process was able to highlight the areas of deepest contrast.

The process itself is fairly straightforward but can be messy. A further print was made using a stronger black and white photograph, in the hopes of achieving a more striking print. This time, Artist’s Loft Prussian Blue ink was used, but surprisingly, the print is green.

I'm much happier with this one, partly because it's one of my favourite photographs.

The technique of creating a digital negative to create a 19th century process is very interesting.