Firstly, Macy says s/he has not found discussion of the different
dichromates in the archive -- look some more, it's there.
Secondly, Terry says sodium dichromate is slower, so don't bother with
it. Where did you get that idea, Terry? From reading the Gloy label?
The sodium dichromate I was asked to test was a 50% solution, but I recall
someone saying it's soluble up to 75% of its weight in water -- in any
event considerably more than ammonium dichromate (which is more than
potassium dichromate). Thus sodium is the fastest dichromate, assuming
you're using an equal proportion of a saturated solution of each.
Since the strength of dichromate is one of the factors in staining in both
plain dichromate stain and pigment stain, it follows that, all other
things being equal, sodium dichromate stains the most, if you're using a
saturated solution.
However, some people (such as Phil Davis) use sodium dichromate in a 15%
solution, which may make its performance similar to the ammonium. Mike
Ware has said that sodium has an affinity to water and might give trouble
for that reason, but in the tests I did (I didn't do prints, only
21-steps) I didn't notice any problems of that kind.
> >I see the Potassium variety refered to the most.
>
The Pictorialists seemed to use mostly potassium dichromate (and it is
cheaper, also not listed as hazardous so in US is easier to get, cheaper
to ship), but most current articles and manuals I've seen speak of ammonium.
I'll mention also that in my own recent work, except for special
situations, I've found that a less than saturated solution of ammonium
dichromate prints better than fully saturated.
On Sat, 13 Jul 1996, Terry King wrote
> Don't breathe it, don't eat and
> if you get on your skin wash it off straight away. Follow those simple guides
> and it will be less dangerous than many things in the kitchen cupboard. But
> remember thany chemical can be dangerous if misused even water.
And clean up spills promptly -- don't wait for them to dry and float
crystals around the room.
The "literature" is full of tales of horror of "dichromate disease," skin
lesions and worse among workers in the photo industry from turn of
century -- before it was understood that dichromate is poison. Some
workers could use if for decades with no ill effects, others were
tormented, actually unable to return to work. Either way, nobody should
*ever* put their hands in dichromate solutions, or in wash water either,
which still has millions of ions. Chrome is one of the two most
allergenic substances known to humans (other is turpentine), so why tempt
fate?
Cheers,
Judy