[Alt-photo] The end of dichromate?

Jorj Bauer jorj at jorj.org
Mon Oct 5 13:31:10 UTC 2015

Well, we might look at the CAS data for both.

First up, Ammonium Dichromate, aka Chromic acid (H2Cr2O7) ammonium salt, 
CAS 7789-09-5:


Some highlights:

Oxidizing solids (Category 2)
   Carcinogenicity (Category 1B)
   Germ cell mutagenicity (Category 1B)
   Reproductive toxicity (Category 1B)
   Acute toxicity, Inhalation (Category 2)
   Acute toxicity, Oral (Category 3)
   Specific target organ toxicity - repeated exposure (Category 1)
   Acute toxicity, Dermal (Category 4)
   Skin corrosion (Category 1B)
   Respiratory sensitization (Category 1)
   Skin sensitization (Category 1)
   Acute aquatic toxicity (Category 1)
   Chronic aquatic toxicity (Category 1)

Risk of explosion by shock, friction, fire or other sources of ignition.
Very toxic to aquatic organisms, may cause long-term adverse effects in 
the aquatic environment. May cause cancer. May impair fertility.

The specific warnings for Ammonium Dichromate are numerous and dire. 
It's understandable why we have such a wealth of information on this 
substance, as it's been instrumental in so many industries and is also 
so dangerous; we needed this information to safely handle this stuff.

Up next we have DAS, aka 4,4'-diazidostilbene-2,2'-disulfonic Acid 
Disodium Salt, CAS 2718-90-3:


Some highlights:

     S22:Do not breathe dust .
     S24/25:Avoid contact with skin and eyes .

     May cause respiratory tract irritation.

     May be harmful if absorbed through skin. May cause skin irritation.

     Not a hazardous substance or mixture according to Regulation (EC) 
No. 1272/2008.
     Not a hazardous substance or mixture according to EC-directives 
67/548/EEC or 1999/45/EC.
No component of this product present at levels greater than or equal to 
0.1% is identified as probable, possible or confirmed human carcinogen 
by IARC.

That's pretty much the entirety of the warnings for DAS. They're similar 
to the warnings for table salt 

While it may be that DAS doesn't have the wealth of scientific study 
behind it that dichromates do, it's believably less dangerous in all of 
the areas in which we do have data (not a carcinogen, not a mutagen, not 
highly flammable, not highly toxic).

-- Jorj

On 10/4/15 12:19 PM, Don Bryant via Alt-photo-process-list wrote:
> I asked first Kees. Tell me why it's better. So far DAS seems like a pig in
> a poke.
> On Oct 4, 2015 12:17 PM, "Kees Brandenburg via Alt-photo-process-list" <
> alt-photo-process-list at lists.altphotolist.org> wrote:
>>> I'm skeptical about DAS being any less polluting than dichromates.
>> Hi Don, what knowledge makes you say that?
>> _______________________________________________
>> Alt-photo-process-list | altphotolist.org
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