Re: question about VDB

In a message dated 11/4/06 8:49:44 am, cryberg@comcast.net writes:

> 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.
> Charles, Portland OR
>
>

Charles

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.

Terry

Terry King FRPS

RPS Historical Group (Chairman)

www.hands-on-pictures.com/

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Received on Wed Apr 12 09:22:10 2006