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  1. #1
    JG Motamedi's Avatar
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    Silver Precipitate with Van Dyke Brown Solution

    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-...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.

  2. #2
    Jeremy's Avatar
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    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
    Let's see what I've got in the magic trash can for Mateo!

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  3. #3
    smieglitz's Avatar
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    Quote Originally Posted by JG Motamedi View Post
    ...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

  4. #4
    davido's Avatar
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    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

  5. #5
    JG Motamedi's Avatar
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    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
    Last edited by JG Motamedi; 04-04-2007 at 10:33 AM. Click to view previous post history.

  6. #6
    davido's Avatar
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    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.

    david

  7. #7

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    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.

  8. #8

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    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.

  9. #9
    JG Motamedi's Avatar
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    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.

  10. #10
    Jeremy's Avatar
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    Jason, thanks for coming back and giving the suggestion about the tartaric acid... I'll pass this along to my student.
    Let's see what I've got in the magic trash can for Mateo!

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