Standardizing Van Dyke Brown Sensitizer Solutions and Mixing Protocols
About to begin my journey into alternative process printmaking, I read Wynn white's Article on the Van Dyke Brown Process and mixed 300mls of the sensitizer formula given therein.
A horrid dirty greenish brown precipitate/sludge formed that settled overnight and was about half of the total volume. A search revealed that this is common and that adding tartaric acid seems to help.
I added 0.5g at a time and stirred with a glass rod. After almost 14grams of tartaric acid the solution still did not clear. I stopped adding more acid. I microwaved some water in a mug to be uncomfortably warm/hot but nowhere near scalding to the touch and placed the bottle in this water. After repeating this process every 5-10 minutes for 5 times, more of the precipitate had clearly
gone into solution. I let it sit for a few hours and when I came back to look the amount of precipitate had gone down to about a quarter of the total volume. However, now there was silver plating on the inside of the glass. Perhaps the heating was uncalled for.
After another thorough stirring and shaking followed by an overnight sit the precipitate reduced to a fifth of the total volume. The silvering is still there. I have never been so far off in mixing anything (developers, fixers, toners etc) and the variability here is causing me some nervousness.
I have the following questions?
1. Does mixing the solutions warm help in keeping tartaric acid levels low? What's the temperature below which silver won't plate out?
2. What is the precipitate? Is it a silver compund?
3. Does tartaric acid convert the precipitate into Silver Tartrate? I imagine that DMAX would be affected if there was more silver per unit solution. If the precipitate is not silver that is being brought back in I could certainly forget about it.
4. Isn't the acidity of the solution increasing by putting in SO MUCH tartaric acid? Shouldn't that change the behavior of the solution w.r.t different papers. If so, what is the Target PH of the standard solution? If not should I add enough to just few a wee bit of precipitate at the bottom. Kind of like mixing Rodinal!
Basically what are the parameters that need to be satisfied for the solution to give good dmax with low to moderate grain.
Thanks a lot,
When mixed correctly, there should be no precipitate in the first place.
Make the three solutions separately: 27% ferric ammonium citrate, 4.5% tartaric acid, 11.4% silver nitrate. Mix solutions A and B together. Now use a syringe to add the silver nitrate solution veeeeeery slowly, drop by drop, while stirring vigorously. This is very important! If you add the silver nitrate too fast you'll get a precipitate, which, once formed, will never dissolve. Add it very slowly (like one or two drops, wait a couple of seconds, add another one or two drops, wait a couple of seconds, and so on) while stirring continuously, and you won't have this problem anymore.