I have received a query off list as follows:
> I am doing photogravure and I saw in the archives a comment that
> potassium dichromate was highly carcinogenic. I read that the powder is
> to be avoided breathing,okay but according to gary kolb's book after you
> sensitize the paper,working with the transfer later gloves arent
> necessary as the chemical is so dilute...but the word highly sticks in
> my mind....I cant find anything in the archives or faq ..as a teacher I
> would expect you to err on the side of caution..do you have an opinion?
And I hope my correspondent won't mind my including his final remark,
which, although I've never seen the process, was affecting:
> The photogravures of the last few weeks have looked so beautiful.I
> wonder if there is anything so beautiful in alt processes as the image
> slowly biting in the acid,watching the tones coming and the image
> changing and darkening...like a daguerrotype..delicate...
I reply onlist, because, although I've worked with dichromates for quite a
few years, and neither I nor any of my students that I know of have yet
gotten cancer, dichromates *are* toxic and deserve utmost respect. Whether
they're more toxic than silver nitrate, or oxalates, or "noble" metals, I
leave to others to say. But perhaps their cheapness leads to carelessness
in a way platinum doesn't.
Firstly, I *think* ammonium dichromate (which is what we use) is more
toxic than the potassium. But secondly, the amounts we use are so tiny
(relatively) that you could probably eat them & never know. (A couple of
years ago someone, I think it was Mike Ware, posted an item about use of
dichromates to preserve sausages for the troops during WWI.)
For years, workers put their bare hands in dichromate solutions, and only
eventually connected terrible skin lesions and poisoning with that
chemical. So, on the normal human premise that two wrongs make a right,
we are scared out of our wits about them now. Let me make some
suggestions:
When you measure and mix your powder wear a dust mask. It's always good to
wear a dustmask when mixing powder, but I would make a particular point of
it for dichromates. Have your water ready-measured at hand, so the powder
doesn't sit in the air while you clean a beaker and pour. Don't shake the
chemical out of the container, which puts powder into the air, but ladle
it out with a spoon, a long-handled spoon if the jar is deep -- I tape a
plastic knife onto a plastic spoon as an extension. If you have a hood
available, so much the better, but few lone practitioners do.
The scale sits on a few sheets of newspaper, so when measuring is done,
any stray powder or liquid can be enfolded & discarded. Liquid spills
anywhere else are also immediately wiped up as the emulsion becomes
powder when dry, which then floats into the air.
NEVER NEVER NEVER put your hands into even the last washwater without
gloves on. I myself, notoriously sensitive in all respects, have extremely
sensitive skin -- I can feel even the last wash water for 24 hours if I
put bare hands in it. You may not have this sensitivity, but why risk
your future? Chrome is the most allergenic substance known for humans,
along with turpentine. Sooner or later almost anyone can become allergic
to it, and then it may be too late.
There are many types of gloves on the market, some quite comfortable. My
rule is to use large ones which slip on and off easily -- much less
trouble. I keep several pairs around the studio, grabbable in a hurry,
because gloves do like to play hard to find.
In addition to wiping spills,the neck and shoulder of the bottle quickly
develop a crust of dichromate, probably because the solution is saturated.
That should be wiped frequently, along with tools and work surfaces. And
don't leave solutions out in the air without a cover. I don't know what
the "biting" you describe consists of, but anything in a tray offers a
broad surface for evaporation. I find that plain corrugated cardboard cut
to size is a big help in confining contents of a tray to the tray over a
reasonable period of time. But for a really long period I'd pour a
solution back into its container (especially in the darkroom).
In other words, my own sense of the situation is that certain basic
precautions should be incorporated into your "chemical" routine,
with perhaps extra care for dichromates. The "toxicity" and so forth
of dichromates may or may not be worse than for certain other chemicals.
Don't take chances.
And speaking of chances, I assume that no one intelligent enough to read
this message would smoke in the darkroom or studio. That's because, aside
from the risks of smoking generally, any chemicals in the air attach to
the smoke and are thus drawn directly into the lungs. (I realize that my
anti-smoking message puts me at risk of being accuset, once again, of
American Imperialism, but I am public-spirited enough to brave the wrath.)
Ammonium dichromate can explode if you encourage it to, or rather force it
to, but in our use that's more a way to charge you $25 for hazardous
material delivery than a real danger. If anyone on the list has had
ammonium dichromate catch fire or explode when they didn't plan it to,
perhaps they'll explain....
Judy