New Rawlins oil print process without dichromate

koraks said:

Yes, since the publication of the Chiba process, people have been experimenting with FAC as a hardening agent in many domains and often with good success. In this application, it works because of the relatively thin gelatin layer and the fact no transfer is required. FAC as a replacement for carbon transfer doesn't work unless a water-permeable oxygen barrier is put on top of the gelatin layer, which is a technical problem that really hasn't been solved satisfactorily yet. However, for a direct pigment/coating process, FAC does indeed work. It's cheap, easily available and safe!

One particularly neat aspect, btw, is that the sensitizer could be incorporated into the gelatin instead of brushed on. This has advantages w.r.t. evenness of coating, consistency/repeatability of the process and overall speed/ease of the process. The main drawback is that the sensitized gelatin and paper of course have to be shielded from any UV light, but in practice, this isn't too difficult.

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NedL said:

I played with this for a while and the linked article solves some of the things that caused trouble. The hot water to prevent bubbles under the gelatin is a great idea. If you can get a good strong gelatin relief "matrix", there are a bunch of neat options... you can ink it like a bromoi (even with multiple colored inks like Gene Laughter ) or with rollers, or ink it and put it through a press....

A few things that might save time if you dive into this:

I found that the kind of gelatin and the pH of the sensitizing FAC/FAO made a difference, as well as some other factors that I never got under control ( possibly temperature / humidity ) so that I'd get a great matrix one day but have trouble repeating it the next, which was frustrating. Also, di-sodium EDTA for clearing was miraculous... I never got 100% perfect clearing with CA or Na Sulfite or tetra Na EDTA. When you play with this you realize that different kinds of gelatin have differing amounts of yellow in them when they dry... the best was "superclear" from Custom Collagen but I never got to the point of getting really strong relief from it. Superclear had troublesome bubbles and adhesion issues... so I never finished refining the process for it. The tricks in this article might solve this!

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xiaruan said:

Recently, I have been studying the CHIBA process. Its principle is the Fenton reaction catalyzed by divalent iron, and the hydroxyl radicals produced cause the solidification of the colloids. Therefore, after the colloids have solidified, all that is needed is to completely remove the remaining iron hydroxide. Thus, I used a low concentration of citric acid as the cleaning agent. After soaking for a period of time, the remaining iron hydroxide in the colloids can be completely removed without any impact on the image.
And recently, I tested the CHIBA process for making gumoil, and the results were also quite satisfactory.

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