From: Neil Miller (neil@miller.gioserve.com)
Date: 01/21/03-02:44:59 AM Z
Hello Joe,
Yes, you are right - it is more of a milkiness than a precipitate. Mine
looks like finely curdled milk after a while, and a thick sludge drops to
the bottom of the bottle. I mix up around 100cc at a time, the A+B mix
together fine - no problem. When I begin adding drops of C you can see a
slight milky cloud as it hits the other solution, but this mixes in OK - I
can hold the mix up and not see any evidence of a deposit. The crunch
factor comes as I have added around 20cc of C sol. - if I don't slow right
down it all ends up like a lime green milk-shake!
Thanks for your reply,
Neil
----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: <neil@miller.gioserve.com>; <alt-photo-process-l@usask.ca>
Sent: Tuesday, January 21, 2003 2:48 AM
Subject: RE: Vandyke brownprints - silvery deposit
Hello Neil,
I just mixed a batch of VDB today and noticed a similar event. The
solutions were mixed separately with distilled water and then combined a bit
at a time with rapid stirring. A+B no problem. As C (silver nitrate) was
slowly added, the combined solution formed a greenish cloud which dissolved
rapidly in solution. The combined solution kept clearing until almost all
of part C was added. With about 25ml to go (solution total of 500ml) the
cloud formed again and remained. I did a test print and it apparently did
not matter if the solution was a bit cloudy. The solution printed well.
I wouldn't refer to the mixture as having a precipitate (which I think of as
something crystalline falling out of solution and settling at the bottom)
but rather it was more like milk, i.e., an emulsion with something very fine
suspended in solution, almost looking like air clouding the solution. (Then
again, I'm not a chemist so my terminology might be askew.)
I suspect the stuff clouding the emulsion is due to excess silver
nitrate-maybe it is very fine silver dispersed in the solution and bouyed up
by all that citrate. I've read somewhere that old VDB solutions that have
some silver precipitating or plating out in the bottle can be refreshed by
adding a bit more tartaric acid to the bottle in order to redissolve the
silver. Maybe that would clear your final mix.
In any event, I'll check the look of my solution tomorrow and if I observe
any change, report back.
Joe
>>> neil@miller.gioserve.com 01/20/03 05:02 AM >>>
...
One thing that continues to plague me is mixing the solutions without
forming a precipitate. I had three attempts over the weekend. All three
had this in common - each part (a, b and c) mixed with distilled water. 'A'
added to 'B' and mixed thoroughly. 'C' added to this mixture drop-by-drop.
The first attempt was at room temp, not very warm at this time of year. As
in the other two attempts, I dropped the 'C' solution through a syringe drop
by painful drop. A bright green milky solution formed, the precipitate
gradually settling a little. 2nd attempt - all solutions heated to 30
degrees centigrade - still a precipitate formed, but much less this time.
3rd attempt - all solutions at 55 degrees, mixing vessel kept in water bath
to maintain temp. No precipitate at all, but next morning a very slight
precipitate had settled at the bottom of the brown glass bottle. This is
the solution I have used to coat the next batch of test paper. Do you think
that the other solutions will be OK if I filter them?
Many thanks once again,
Neil.
--- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.427 / Virus Database: 240 - Release Date: 06/12/2002
This archive was generated by hypermail 2.1.5 : 02/21/03-10:44:17 AM Z CST