VDB - what did I do wrong???

[Kimberly Anderson]

In preparation for making some prints for the alt print exchange, I went and bought new chemicals to make some VDB solution.

I followed the instructions in the 'Keepers of Light' book, mixing the A-B-C forumula like I had a dozen times before.

But...(and here's the rub), my scale that I had borrowed from my mother does NOT measure in 1/10ths of a gram ( 0.0).

I *guessed* reasonably close with the tartaric acid and the silver nitrate, mixed it all up, and when I got A into B and then into C, the solution stayed foamy for quite some time and then started to seperate into a cloudy solution on settling to the bottom, and a nice clear green solution staying on top.

I wondered if the chemicals I'd purchased were the 'right' ones, so I hurried and re-emulsified the solution, drew out an eyedropper full, and coated a sheet of paper.

Force-dried it very quickly so the solution wouldn't seperate during drying, and made a print.

Ironically the solution is provides a very nice black tone, perhaps even nicer than the 'accurate' solutions I've made in the past.

I do not know what would cause the seperating of the solution other than the inaccuracy of the measuring of the dry chemicals.

I guess I could keep it, stirring it vigorously before applying to the paper, and see how the rest of the prints turned out.

Any ideas on what would cause this? I am investigating a more sensitive digital scale.

Thanks,

 

[Aggie]

When you mix the c solution into the a/b one, if you do it quickly it developes a precipatate. As the full solution ages it dissolves back into the solution. Let it age for a week and you will be fine.

 

[Kimberly Anderson]

That's really weird though. I didn't do anything different with the mixing than any other time, and this time it did the seperating.

I have plenty of VDB solution to use in the upcoming week, so it has time to 'age'.

I guess I ought to keep it and see what happens, especially since I'm very satisfied with the tone and Dmax it's giving me.

Thanks,

 

[smieglitz]

I can't remember the source but long ago I read a suggestion of adding a little more tartaric acid if the silver was precipitating from solution. I don't know if that would help solve your problem, but I'd let it age and then try some additional acid before you toss it out.

Joe

 

[Kimberly Anderson]

Joe,

Thanks for the info. I do not understand what happens chemically when the solution is made...I am not a chemist, nor do I even play one on TV.

I am getting the feeling that I will begin to be a chemist, insomuch as I have a curiosity now about what happens and how this all works.

I noticed that in the 4-ish hours that I let the solution sit yesterday, that the amount of cloudy sludge on the bottom of the cup had gone down.

Either it had settled, or it had started to be absorbed into the solution.

I have heard that aging the solution a bit is a good thing, not only from Aggie, but I think I read it somewhere too.

I'll watch it and see what happens.

Any chemists here who can explain what is happening?

 

[Ole]

Any chemists here who can explain what is happening?

I'm a chemist, but that doesn't always help...

My guess is that as the three solutions are mixed, the concentration of something-or-other locally rises above the solubility. By mixing very, very slowly or letting the mixture age the "sludge" goes into solution, as the overall concentration is below the solubility limit.

That's why I love my magnetic stirrer