Gum Bichromate Printing Reversal Demonstration

Here are two early samples which demonstrate the problem of a gum bichromate print where the resulting print has reversed out to a negative. The original negative is 4x5 shot on Tri-X film. Ignore the dust marks etc. on this first print as it was taken from a poor quality contact sheet, however, it will serve as a reference point for what the final product should look like.

Now, here is the same negative printed on gum bichromate -- as you can see, the level of detail is quite good. The gum print was made using an emulsion mixed as follows:

• 2.5 ml gum arabic solution


• 2.5 ml potassium bichromate solution


• 0.5 gm Daniel Smith Lamp Black watercolour pigment

The problem is that Lamp Black is a very heavy pigment and 0.5 gm is way too much for this amount of emulsion. You can see that the image has reversed itself to negative. The emulsion was coated on Lanaquarelle Medium Watercolour paper (140 lb.) and the print was exposed for 20 minutes under a #2 blue photoflood lamp in a reflector about 25" away from the print.

Partial Success?
Here's what happened after I switched to Daniel Smith Burnt Umber using similar amounts of gum and bichromate as before. It still reverses!! The amount of pigment was approximately 0.1 gm. although it is difficult to measure such a small amount even with my triple beam balance. I should also note that the gum arabic solution used for these first three prints was made up from gum powder. I'm not sure about the percentage solution, but it is quite thick.

At this point in my testing, I switched to the premixed gum solution sold by Photographer's Formulary. Finally, I got success with the same formula as before, however, the contrast level and exposure are not acceptable.