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Gumbichromate
Photographs from Pinhole Camera Negatives.
Gumbichromate is an excellent photographic process for creating your own Photographs. This is especially so if you are making the pictures from from Pinhole Camera Negatives. The whole process of making the picture is very much within your control. You build the camera, make the exposure, process the negative, make the printing paper, print the negative and finally manipulate the print processing.
Chiaverano, Italy. 1982 Gumbichromate print from a 5" x 4" pinhole camera negative
To make these pictures I built a wide angle pinhole camera out of art mounting card which was cut to shape, glued together and then taped with black sticky tape at the edges to ensure a light tight box. (Link to the design) I used Kodak Gravure Positive cut 5" x 4" sheet film. This has the advantage of a thick base, slow speed, low reciprocity law failure and can be easily processed in red light conditions using a normal print developer. The print is then made by mixing a saturated Potassium Dichromate solution with artist's gum arabic. The colour is achieved by adding poster paint to the mixture. This is then brushed on to thick art paper and allowed to dry in dark conditions.
San Stephano: remains of a 10th Century Church. Chiaverano, Italy. 1982.
Gumbichromate print from a 5" x 4" pinhole camera negative
The print exposure is made by contact printing the negative using exposure to bright sunlight for a few minutes. The emulsion is sensitive to UV light and needs quite a lot of exposure. The print is processed by floating the paper face down in a dish of cold water. The unexposed areas, the highlights, are soluble in water and so gently fall away from the surface of the print revealing the paper. The exposed parts of the picture are rendered insoluble by the UV light and therefore remain on the paper surface. It is possible to add further control to the picture by brushing the surface of the print lightly to modify the shadows and the highlights. The final stage in the process is to stick the wet print to a piece of wood using gummed paper tape so that as the print dries out it will stretch itself flat by shrinking.
