Yesterday I mixed a batch of Wynn White's "ABC" Van Dyke sensitizer. As I added the last few milliliters of Silver Nitrate solution (Solution C) to the previously mixed Ferric Ammonium Citrate (Sol. A) and Tartaric Acid (Sol. B) a silvery-white precipitate formed.

It is an odd preciptate, a suspension with a curdled milk look. I mixed the solution twice more and each time had the precipitate. I assume that the precipitate is insoluble silver-something caused by too much silver nitrate in the solution.

I found a similar problem reported by Neil Miller: http://www.usask.ca/lists/alt-photo-process/2003/jan03/0479.htm

It did produce a decent VDB print this afternoon, so should I filter and forget?

Thank you in advance.

jason

ps: for the record I am using distilled water, my beakers are clean, and my chemicals are all fresh and have all worked in other applications.

Jason, I had a student today experience the *exact* same thing! I had her filter the solution and then print a negative she knew printed well in VB... came out just like normal... weird stuff happening here in Southern North America :)

...I assume that the precipitate is insoluble silver-something caused by too much silver nitrate in the solution...

Jason,

I don't remember the source or even if the precipitate problem was in Clerc's gold toner rather than the VDB emulsion, but my problem many years ago was solved by adding a bit more tartaric acid to the mix.

I also just read a thread on the alt list where someone added 100x too much tartartic acid to Clerc's gold toner with no great harm. So I doubt adding slightly more to the vdb emulsion would hurt.

Joe

Jason,

Did you add the silver nitrate very slowly as you were stirring? I've noticed this precipitate every time I pour a very small amount of silver into the AB solution but it dissapears as I'm stirring. Also, I always strain it the next day with an unbleached coffee filter.
As for the Tartaric Acid toner incident (yes, that was me), I received some info from Bob Schramm (on another forum) that because that particular toner is already acidic, then extra acid wouldnt effect ph level and, therefore, should not effect toner. But VDB sensitizer is a completely different thing, I'm not sure of it's ph and how the acid would effect it.

david

Thank very much for the answers. On my second and third attempts I did pour the AgNO3 solution very slowly as I was stirring. It didn't change anything.

I will try adding a bit more Tartaric Acid, per Joe and Davido's commments, and see what happens.

I heard from Neil Miller, who had a similar problem. He thought that either impurities in the Ferric Ammon. Citrate or the acidity of the Silver Nitrate was the problem.

Thanks again,

jason

My guess is it is probably the FAC. Ferric ammonium citrate is what they call an ill-defined chemical, in that it has no single chemical formula. I have heard of some people having problems with certain supplies of FAC.
I just ordered some Brown FAC from B&S. Apparently it has a higher percentage of Iron and produces better dmax. Perhaps it would mix better?
Dana Sullivan from B&S recommened it in this older thread (http://www.apug.org/forums/forum42/35317-brown-green-fac-vdb.html).

david

I have that same thing when I make vandyke solution. I just add more tartaric acid and shake until it clears. I haven't noticed any problem with that.

I almost always have a sediment of some kind in my VDB sensitizer. I just let it settle to the bottom of the bottle, and try not to "stir it up" when taking the sensitizer up into the dropper.

Also, I think ferric ammonium citrate is a pretty well-defined compound, as is ferric ammonium oxalate. Ferric oxalate (without an ammonium counter-ion) is supposed to be somewhat ill-defined. My guess is that the white milky material that initially forms as the silver nitrate is added to Wynn White's "AB" solution is probably silver citrate or silver tartarate that dissolves in the excess solution.

I added some tartaric acid to the mess and the precipitate went back to solution. It seems to print about the same as it did before adding the acid.

Many thanks for advice and help.

Jason, thanks for coming back and giving the suggestion about the tartaric acid... I'll pass this along to my student.

I have the same problem. After reading this thread I mixed a modified version of Wynn White VDB solution, with 20% more tartaric acid and a little bit more water:
A 40ml H2O 9g FAC, B 40ml H2O 1.8g TA, C 40ml H2O 3,8g SN.
and again I have the same white precipitate.
Please, can you tell me how much tartaric acid you added to the solution?
Thank you
fabiano

Fabiano,

I added quite a bit of Tartaric Acid, maybe 2.5g. I just kept adding .5g of the acid, stirring, and waiting for 10 to 15 minutes. As I recall it took five rounds to dissolve everything.

For what it is worth I made two batches; one which I added Tartaric Acid, and the other which I just filtered. Both work identically.

I added some tartaric acid to the mess and the precipitate went back to solution. It seems to print about the same as it did before adding the acid.

Many thanks for advice and help.

Adding acid to the solution usually clears up the precipitate. So long as you add just enough to clear the solution there should be no change in printing characteristics.

Sandy

Thank you for your answer. This morning I added 1g TA to my modified solution and this eliminate almost half of the precipitate. I added 1g more and there was no more precipitate, but the solution was still milky and opaque. I tried with 0.5g more but it does not became transparent.
This morning I print something. It is washing thus I have to wait to give a final judgment, but I fell the new solution with much more TA is much slower, a little bit grainy and high contrast. A big difference is that it develop much more than the standard solution.
I have the feeling I prefear this solution more than the standard one.
I will run more serious test to adjust the amount of TA and I'll post my results here.
Thank you again
Fabiano