We recently acquired some and I began experimenting with it in the Ziatype process. I had a private workshop last week for two printers from the NYNY area and we experimented with the Tween 20. I also gave David Kennedy a bottle to try with his traditional palladium printing. Well, I have to say that Mike is sure right about this stuff, it is the magic bullet of platinum printing.
First point I want to make is that there is no set amount to use, just a point at which there is too much. Too much will cause small wavy like ridges to form where the sizing has been broken and the emulsion has penetrated too deep into the paper. For Ziatypes we found that you could coat a little bit wet and then let the paper sit for a few minutes, any uneveness in the coating would invariably even itself out as the paper sat. The Tween 20 seems to first flow the emulsion and then pull it down into the paper. Too heavy a coating has been deadly with the Ziatype, as it is a printing out system and is self masking. Because of the masking, the depth of the emulsion is thin and any wash-off will cause mottling. The Tween 20 prevents any surface emulsion building up by pulling it into the paper, thus allowing heavier coating and which in turn give better dmaxes. We pulled dmaxes up from 1.35 to 1.50 on Ziatypes with the use of Tween 20.
David Kennedy reports using 25 drops of 50% Tween 20 to 25 ml of water, quite dilute compared to what we were using. I suspect there is a long plateau where almost any dilution works as well as any other. Kennedy says he is getting much better dmaxes and has suggested that we actually put it into our emulsion products. This I suspect is not a good idea as the Tween may break down over time due to chemical interactions and it is also a good idea to let the individual printer control this variable.
I'll let Kennedy relate his experience with Tween 20 if he wishes.
Since non-silver printing depends a lot on each printer's personal variables and environment, some experimentation will be needed to find the right concentration and usage technique for Tween 20. Mike Ware is to be commended for all of his contributions to alt-photo world, this is just a small but important one that needs to be exploited further. I've also been told by Sil Horowitz that the various Tween numbers (20, 40, 60, and 80) are interchangeable in photography, so if you can't get Tween 20, one of the others will work just as well.
Sil says:
>The numbers represent molecular polymerization - the higher the number, the
>greater the polymer. In photography, this doesn't seem to mean anything, but
>it is very important in the emulsification processes, as well as in
>detergents.
Just thought I'd pass this tip along to the List.
Dick Sullivan
<center>Bostick & Sullivan
PO Box 16639, Santa Fe
NM 87506
505-474-0890 FAX 505-474-2857</center>
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