RE: Ammonium Dichromate

On Wed, 29 Dec 2004, Loris Medici wrote:

>
> Probably the emulsion will be able to hold more pigment since AD can't
> harden (evaporated-by-the-time-of-exposure) water... I haven't read any
> recommendation other than 1:1 or 1:2 for gum.
>
> Regards,
> Loris.

If I remember correctly the official solubility for ammonium dichromate is
31 grams to 100 cc water at 68 degrees Fahrenheit, & tho I am a
Centigrade-impaired American, I believe that's 20 degrees C. For that
reason I always mix it at 26 grams to 100 cc to allow for temperature
change, BUT THAT'S JUST A HANGUP, IT DOESN'T MATTER. The old books tell
you to put a pound of potassium dichromate in a jar, top it off with
enough water to rise above it, and keep adding water as you use solution,
and always have the same saturated solution, but that doesn't matter
either.

Hand coating and the variables of development give so much leeway that 5%
or 10% more or less dichromate is irrelevant... but we have been brain
washed in photography to establish CONTROL... However, that actually kills
brain cells (as has been proved by the latest research), besides being
impossible.

I'll add that I generally dilute my dichromate solution by about 1/3 water
in use... I find a weaker solution coats better and generally works
better. And depending on what you need, the ratio of gum to dichromate
solution can be anywhere from 1 to 2, to 2 to 1 (Betty Hahn used that in
one article). It was often 2 parts gum to one part potassium dichromate in
the early 20th century, until Paul Anderson came on the scene with his 2
or even 3 parts 100% sodium dichromate to one part gum in the 1930s.

When I learned gum in the early 1980s, 1 part gum to 2 parts dichromate
was the norm -- but gums vary also, so those figures are highly
approximate. It isn't rocket science anyway. (But it works better than
rocket science, so that's a good thing.)

Judy
Received on Wed Dec 29 21:04:08 2004