[alt-photo] Re: VDV

[Christina Anderson]

Ken,
Below is what the archives say about this issue. Sorry I don't have time to edit and correct, and it is a bit of a mishmash, but maybe will be of help (NOT MY WORDS):

I made a batch with my old favorite formula and got a heavy amount of yellow precipitate in the bottom of the beaker. I put a little citric acid in a sample of the cloudy solution and it cleared almost immediately. Sullivan

Without the tartaric acid, you will get a substantial precipitate of silver
citrate, which wastes silver and makes proper coating difficult. The tartaric acid keeps the silver
in solution.

My guess is that the yellow crud
is silver tartrate. An excess oxalic acid in Kallitypes causes a yellow precipitate to form which is silver oxalate. Guess is that it is throwing off iron, or
iron oxide as ferric compounds are wont to do.Dick Sullivan

If you get the precipitate slowly add more tartaric acid until it dissolves. It usually won't take much. Everything will be fine and it will print nicely.The additional tartaric acid did the trick (i.e. dissolved the precipitate). However, it didn't happen right away. In fact, when I added my last little bit of tartaric acid (mixed in a bit of distilled water) to the VanDyke solution, I was disappointed at the lack of results. I put it back in the chemical cupboard with the expectation that I needed more tartaric. To my delight, when I checked the solution two days later, the precipitate was gone.

 think what you mentioned here is the whitish precipitate, which I take as
undissolved silver, and which does dissolve with the addition of tartaric
acid. However, the silvery colored plated silver is a different matter; no
matter how much tartaric acid is added (I even added some ammonia), it
would not disappear. This loss of silver from the solution definitely would
not help but reduce print density, and that would explain why the freshly
mixed solution would give greater density. Sam Wang

Vandyke is one solution that I do not agitate 
once it has been mixed. It is best not to try to print with the dregs of the 
solution. 
Sarah

One thing that did interest me about the previous postings was the mention 
of a precipitate forming upon addition of the Silver Nitrate. I almost 
always got this when using distilled water (sold as auto battery top-up), 
but never get it using the purified version from pharmacies. It always used 
to mix in to leave a clear solution with either water type but was 
definitely worse with the distilled water. I suspect many commercially used 
water distilling appliances actually are just water softeners using NaCl .

Heat to 130º to have precipitate go into solution, or heat water when mixing.

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'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. Joe

My conclusion after once enthusiastically filtering the 'sludge' from 
vandyke solution some years ago, was not to do that again. I concluded that 
I had filtered out some of the silver. On exposing the filter paper to 
light, dark spots appeared and the paper went brown. I am pretty sure that 
the filtered solution then printed poorly. I never did that again.

This is pretty common. All of my VDB solutions have plated, though I 
think it took quite a bit longer than two weeks. But if if prints ok 
then it is ok and in my experience the plating has not seemed to 
detract from printing qualities. Sandy King

Extra doesn't seem to hurt so you can increase the amount of
tartaric acid by about 20% and the silver precipitating out and all of that
will go away.

If you get the preciptiate, just
keep slowly adding tartaric acid until it is all dissolved.--Dick Sullivan
Christina Z. Anderson
christinaZanderson.com

On Oct 10, 2012, at 4:54 PM, Ken Sinclair wrote:

> HI All
> 
> Today, I experienced something that I have not 'met' before.
> 
> On mixing up a fresh solution for VDB printing, just as the last of the silver nitrate volume 
> was being (all so very slowly) into the 'mix' of FAC and Tartaric acid, I seemed to get a very light
> green precipitate that has now slowly dropped to the bottom of my brown bottle.
> 
> I have NEVER seen this before. Could someone offer an explanation?
> 
> Do I have to 'start' all over again?… or will the light green precipitate re-dissolve with time?
> 
> TIA
> 
> Ken
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