[Alt-photo] Re: DAS

[Kees Brandenburg]

Hi Keith,

I started using powdered casein, 4 gram in 25 ml cold water. After a 1 hour soak I am adding 1 gr ammonium carbonate in a little (1 or 2 ml) water. Warming this 'au bain marie'  and stirring until most of the bubbles are gone results in a fairly thick casein paste. 
I started testing with a 1:1 mix of this casein preparation with a saturated 3% DAS solution and lampblack watercolor pigment. After some tests I started cutting down the DAS concentration and am using a 2% solution now. Lower concentrations might work too. With this mix I can print negatives with a lot larger density range than I am used to with gum. My first tests were dissappointing because of a too low negative contrast and a too high sensitizer concentration. Printing times are (much) shorter than with dichromates.

Kees

On 12 apr. 2013, at 21:29, Keith Gerling <keith.gerling at gmail.com> wrote:

> I purchased some to use with casein.  I haven't tried it yet, but I'm happy
> to hear you've had good success with it.  Would you mind sharing your
> casein procedure?
> 
> Keith
> 
> 
> On Fri, Apr 12, 2013 at 1:37 PM, Kees Brandenburg
> <workshops at polychrome.nl>wrote:
> 
>> I was wondering if there are people on the list who participated in the
>> DAS group buy that was organized some time ago.
>> DAS is the acronym for 4,4'-Diazidostilbene-2,2'-disulfonic acid, disodium
>> salt, tetrahydrate and is a non- or less toxic replacement for dichromates
>> in carbon printing. I am using it for some years now and am quiet happy
>> with it. Most handy is the non existing dark effect. Carbon tissue can be
>> made presensitized. This speeds up printing a lot.
>> 
>> Recently I also tested it with casein and found out that it works
>> extremely well!  I am looking forward hearing other people's experience
>> with this powder!
>> 
>> Kees
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