Vandyke solution : white precipitate ?
I made my first small batch of Vandyke, and I have a seemingly insoluble white precipitate in it.. Is it normal ? Is it the reason the solution has to "age" ?
I use deionised water (distilled is hard to come by around here).
44ml + 6g Ammonium Ferric Citrate
+ 1g Tartaric Acid
Another solution with:
+ 22ml + 2.5g of Silver Nitrate
Then I used a seringue to very add the silver nitrate solution into the other one, stirring all the time.
A precipitate (fine whiteish powder) formed, and no amount of stirring helped..
I left it to "age" but I really don't know if it's supposed to happend...
Allright, after quite a bit more digging, it seems it's a "common" problem and can generally be ignored. I also found a "cure" where apparently adding a tad more Tartaric Acid to the solution will clear the precipitate out, eventually.
But the general consensus is that it doesn't affect the prints!
Just to conclude on this narcisic topic and to help for general "search" result quality on the forum...
I added some Tartaric acid (tip of a teasooon) directly in the brown bottle, and shaked. 10 minutes later, the precipitate was gone and the solution got the "all clear"
From what I understand the precipitate would in fact lower the amount of "reactive" silver in the solution; adding Tartaric acid bonds that remaining silver back into Silver Tartrate.
As to why the proportions were sufficiently wrong in the first place, I have no idea. Insufficient purity of the tartaric acid ?
Interesting. I made up 300ml of solution in July and have always had the same precipitate. I basically just shake the bottle now and again and before using it make sure it's sat for a bit so things settle out. The plan was basically to just throw it out when it got too sludgy, it's cheap. :-)
The problem is the Green Ferric Ammonium Citrate. It is considered an "Ill defined chemical" and is actually a collection of closely related chemicals. At Bostick & Sullivan we use only Brown Ferric Ammonium Citrate when mixing Vandyke solution, which eliminates the Silver precipitate.
Using the Brown Ferric Ammonium Citrate also extends the shelf life of the solution, eliminates the white precipitate, and produces an image with considerably better mid-tone separations and not the harsh contrasty look of the Green Ferric Ammonium Citrate version.
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Thanks Dana, I think it was one of your post back on the mailing list archive that gave the tip on how to clear it out...