[alt-photo] Instability of dichromate, et al...was Re:"Moistened"

[Judy Seigel]

On Fri, 8 Jan 2010, Trevor Cunningham wrote:

> Yikes!
>
> Never realized AD was so unstable!

I haven't followed the reasoning behind the theory that Am Di is "so 
unstable," but I do remember a report in the early days of the list... The 
finding (and, no, I don't remember who "found" it, tho it could have been 
someone still here, in which case, hello?) -- tho, as I was saying, the 
finding was that in order to get an "explosion" of any sort from ammonium 
dichromate, it had to be hammered with a metal hammer in a metal frying 
pan. Which is to say, if you're scared of gum, I can't really blame you 
because non-gum printers tend to make such a holy shrek of the process... 
But explosion....? Not. So put on your hazmat suit and try, just TRY to 
get even a little bang (without setting a match to it, anyway).

I myself have lived, slept, shouted, and PERSONALLY EXPLODED, not 
to mention jumped up & down, cursed & rent my garments on numerous 
occasions in a room with lots of ammonium dichromate, especially the dry 
powder (here being called "crystaline"??), but other forms as well, and 
never got so much as a hiccup out of it.

Now someone said they used 9-year old am di (I don't recall whether powder 
or solution was specified), but I'm not surprised. In fact I haven't found 
any expiration date for the stuff. When they were closing out a chemical 
lab at school, maybe 10 years ago, I inherited a half-full bottle of am di 
powder, which from the looks of the bottle dated from the early 1900s, if 
not earlier. Not to mention that when you buy am di, especially from a 
source without a lot of turnover, that bottle of powder could have been on 
the shelf since 1935 -- the last surge of gum printing before this one.

Recently, finding my studio in a shambles (if you could believe) and 
unable to locate my usual am di, I started working from this decidedly 
ancient stash.  As far as I noticed, everything behaved as usual.

But my point here is also one I've made before:  Gum printing is NOT 
rocket science... and we probably still don't know all the variables -- 
effect of the paper, the size, the ratios of the mix, degree of soaking 
into the paper when applying the coat, temperature and humidity, interval 
between coating and exposure, light source, development (temperature, 
agitation, duration, perspiration, effects of which are varied by all the 
above factors, among others, including ingredients of the paint: pigments, 
fillers, dispersal agents... omigod, *especially* dispersal agents), age & 
source of the gum, and probably esoteric effects like what you ate last 
night and how recently you bathed. Not to mention what the folks at the 
pumphouse have injected into today's water.

Speaking of pigments, however, some are death in gum, some are swell, 
which you can't know for sure unless you have the pigment number, not 
just, for instance, "alizarin crimson." And supposedly identical pigments 
can be manufactured from different chemicals in different mills.... and so 
on, ad infinitim. (I remember using a color in acrylic paint, maybe 
"Venetian red," which, when I'd finished the jar, was no longer available 
from the same source, that particular mine having run out. I eventually 
found a paint with the same name, but it was different across the board.

Not to mention that variations of development can be equally operative-- 
or more so...

In other words, strike "instability of dichromate"from your worry list.

Judy