Re: Gum prints with screen printing sensitizer?

Andy Schmitt

Tea has more caffeine than coffee does... green tea perhaps...


Andy Schmitt PPA

Head of The New & Improved Photography Dept,
Peters Valley School of Craft

-----Original Message-----
From: Alt-photo-process-list [mailto:alt-photo-process-list-bounces@...] On Behalf Of tdp
Sent: Wednesday, March 19, 2014 9:13 AM
To: alt-photo-process-list@...
Subject: Re: [Alt-photo] Gum prints with screen printing sensitizer?

Kees! That is extremely useful information, and a link to some wonderful prints as well :) I had no idea that the polysaccharide structure was the problem printing gum with DAS, although no manufacturer in the US will send me DAS so it's kind of a moot point.

One thing to note, I think Greg pointed it out in that APUG megathread, is that there is no free formaldehyde in the ProChem sensitizer, the molecule is either a (here my poor chemistry skills start to hurt) condensate or a precipitate of 4-Diazodiphenylamine and formaldehyde. If there was free formaldehyde it would certainly be classified as a carcinogen here in the states!

I have no doubt that your sources are correct about the toxicity of the screen printing diazo sensitizer. I would certainly not call it non-toxic, the MSDS clearly states that it is toxic by oral ingestion - although it's apparently 10 times safer than caffeine. (Actually, the caffeine MSDS is super scary, maybe I should switch to tea.)

Since wastewater disposal is my first concern, the fact that it isn't ecotoxic makes all the difference between diazo and dichromates. I also don't think it would be wrong to say that this chemistry is substantially less hazardous than dichromates as far as human safety - there's a reason why commercial screen printing moved away from chromium!


On Wed, Mar 19, 2014 at 4:48 AM, Kees Brandenburg

On 17 mrt. 2014, at 17:37, tdp <tdptdp@...> wrote:

its CAS number is 41432-19-3
Hi Travis,

My Chinese DAS supplier also sells CAS 41432-19-3
(4-diazodiphenylamine sulfate ) but he told me it is more hazardous:
"Hi Kees, DAS is non-toxic, it's absolutely green. However, the
4-diazodiphenylamine sulfate is hazardous. We suggest you give it up."

Prochem's MSDS for CAS 41432-19-3 also mentions it's toxicity:

"SYMPTOMS OF OVEREXPOSURE for each potential route of exposure:
Inhaled: Signs and symptoms of excessive exposure may be to the
central nervous system.
Do not inhale the powder.
Skin: May cause allergic reaction and skin irritation/Eye contact:
moderate irritation harmful. No quantitate data available."
Swallowed: Harmful, no quantitative data available, toxic.

I'm also a bit worried about the formaldehyde component in the molecule.
It might introduce unwanted hardening in gelatin and re-introduce the
"dark effect" known from dichromates.
DAS has no dark effect on gelatin and I have months old sheets of
presensitized carbon tissue that still print perfectly today. DAS does
not work with gum arabic because of the polysaccharide nature of gum arabic.
Casein and Gelatin, being proteins, do.
It's interesting to know this diazo compound hardens gum too!

I have been printing casein with DAS and it prints very fast! Some
examples here:, the text for this workshop announcement is in dutch).
Next zerochrome casein/DAS workshop in my studio in the Netherlands :
weekend of April 12 and 13.

The speedball sensitizer is a different diazo compound:
Polymethylene-p-Diazo Benzene Dye (CAS #71550-45-3) and it also
contains Phosphoric Acid (CAS #7664-38-2)
There are some interesting remarks about it at the beginning of this
long APUG thread about DAS:


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