RE: question about VDB

Terry,

>

     Many, but not all of the formulas call for dissolving all of each
chemical, separately, in a third of the water. Thus, 27 grams in 100 ml etc
and finally mixing them. I use 33 ml lots to make a total of 100 ml at the
end.

I needed to get from my sick bed back to the studio before I tried to
consider the question. As you suggest, the amounts should be

9 g of FAC in 33 ml of purified water
1.5 g of tartaric acid in 33 ml and
3.8 g of silver nitrate in 33 ml.

Given that I have never had problems with precipitate I wondered what could
be going wrong when other people did.

I am not suggesting that any of these apply to other people's practice, but
things that can go wrong include:

contamination of containers with other chemicals or tap water for which one
should always wash the containers in purified water and then dry them to
reduce the risk

contamination of tools,brushes and rods from even a single grain of another
chemical

getting the sums wrong

confusion of grains for grams somewhere in the calculation

using tap water instead of distilled or purified ( silver nitrate solutions
will go white when contaminated with tap water as the chlorine in the water
will change silver nitrate to silver chloride).

That this list can go on and on is an indication of how important it is to
be very very careful even with such a simple process.
>

While all of what you say is true, I think the fact that Charles, Loris, and
myself have all observed the same results of precipitate when adding the
final volume of silver nitrate solution (part C) to the mixed parts A and B
is an indication that this is a common occurrence in fact an expected one
based on our experience.

Perhaps some of our experienced VDB printers can comment one way or another.

Don Bryant

 
Received on Wed Apr 12 09:44:06 2006