From: Judy Seigel (jseigel@panix.com)
Date: 08/22/02-10:04:26 PM Z
On Wed, 21 Aug 2002, julian smart wrote:
> Hi,
> one thing I have noticed when doing a batch of VDB prints, is that if I mix
> all three solutions together to make a single working solution it just
> doesn't last. It seems to go off (oxidise?) and makes producing a decent
> print impossible even the next day.
> I tracked the problem down to the tartaric acid, having found that the other
> two solutions will keep well for months in dark brown bottles. The tartaric
> acid solution will not work even the next day. I figure the cost of the
> tartaric acid to be almost negligible and therefore mix this fresh before
> any printing batch- a bit of a pain, but I always get a decent result.
>
> The f.A.citrate, btw , will always generate a certain amount of sludge on
> storage. I have found this to be harmless to my prints as long as it is not
> disturbed in the bottom of the bottle..
Just because the tartaric acid doesn't keep well alone in solution
doesn't necessarily mean that's what's causing your sludge. You could of
course have some defective tartaric, but the amount used for VDB would
make a very weak acid and weak solutions don't keep as well as stronger.
For what it's worth, I normally use VDB solution YEARS old -- I stopped
printing VDB regularly when I still had a half bottle full, and from time
to time in the years since have used it for a layer, or whatever (even a
"fancy border"). The emulsion often shows a black precipitate which goes
back into solution during coating & the prints are as good as ever.
My guess would be the trouble is either fake "distilled" (not uncommon),
problem ferric ammonium citrate (which is often borderline), or you're
keeping it in plastic, not brown glass (possibly all of the above).
However, what you're calling "sludge" in ferric ammonium citrate sounds
like the crust or mold that forms on the plain solution (solution A in
cyanotype). This only happens once, IME, so you can filter it off -- but
it doesn't happen at all when the 3 solutions are combined.
Judy
This archive was generated by hypermail 2.1.5 : 09/19/02-11:02:50 AM Z CST