What's your workflow for Gum Bichromate printing?
I did some successful gum prints this summer. I was shooting wet plates and didn't have much time to spend with other techniques. But I had a few good prints and I thought "ok, the pigment is working, sensitizer is ok... let's resume this later"... Unfortunately I didn't take note of what I did, thinking it was very simple to replicate.
I was wrong! I can't get a good print now! I don't know why...
I tried several combinations of pigment/gum/sensitizer but nothing worked well... The prints didn't clear very well or they were too contrasty or too flat...
What I did a few months ago were just 1 coat /1 layer / 1 pigment prints and they were fine (ok, not great tonal range, but overall ok...). I want to replicate that result before going any further and try multiple layers / colors. I'm using MaimeriBlu pigments and they should be ok. I've started with Carbon Black and that's the pigment I used with success.
First, I size my papers with gelatin. I don't use formaldehyde for hardening, just aluminium potassium sulphate, which is less toxic. It worked before.
I used to have Winsor & Newton gum, but I ran out of it and since then I mix my own from gum acacia lumps. But I can't remember the dilution I used. I found many sources on the internet, but it's not very clear... I tried 15 to 30% mix. Now I just diluted another batch 1:1 with distilled water, it took a while to mix.
About the sensitizer, I use potassium dichromate, in 12% saturated solution. I always use distilled water of course.
Now about the pigment-gum-sensitizer mix... I normally mix gum and sensitizer 1:1. But I don't know how much pigment to use. If I mix 1 g of pigment (MaimeriBlu carbon black) each 10 ml of gum (or 20 ml of gum + sensitizer mix) , the solution is too liquid and doesn't coat very well... The pigment remains at the edges of the paper with little on the middle (just streaks with a greenish-yellowish tint from the gum+dichromate). If I double that amount, the color is more uniform. I know that many build up the density by adding layers of gum... But I want to do what I did this summer and get basic decent prints with only one layer. That was a good starting point.
I just coated some papers with homemade 1:1 gum solution, dissolved again 1:1 with potassium dichromate sensitizer and 2 g of pigment each 20 ml of gum+sensitizer mix. I stirred the solution very well and coated the papers. The coating was thick and the color uniform, with little streaking (which I think it's normal) and a glossy surface. I will expose these papers tonight and let you know.
In the meanwhile, is there an expert on gum printing that can give any advices? I think the material I'm using is ok because it produced good results in the past. What I can't figure out must be the dilutions and pigment/gum/sensitizer ratio...
Last edited by Fulvio; 09-26-2007 at 12:26 PM. Click to view previous post history.
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