Van Dyke sensitizer issue

glbeas · Jun 8, 2020

Im wondering if anyone has had the sensitizer precipitate out a black fluffy sludge after its been in the bottle for several days. I had this happen to mine. It was still working fine as far as I could tell so I ran it through a coffee filter. Id love to know what was going on with the sensitizer and what can be done to prevent that. It was mixed with distilled water following the formula I got from Jaques Kevers publication “The Iron Silver Processes” which I think is a pretty standard formula.

fgorga · Jun 8, 2020

Just a guess... silver oxide

Silver oxide is not very soluble in water near neutral pH although it is reasonably soluble in acidic or basic solution.

Silver oxide is black... think tarnish on your grandmother's silverware.

I would keep the bottle of sensitizer tightly sealed and avoid vigorous stirring or shaking which will aerate the solution.

glbeas · Jun 8, 2020

So the tartaric acid in the formula was not enough to prevent this? Are there other formulas that are more stable?

fgorga · Jun 8, 2020

I don't think that the tartaric acid is present to prevent the oxidation of the sliver. Rather, the tartaric acid is these to complex the iron(III) and increase its photoreactivity...i.e. it serves the same purpose as oxalate does.

The publication you cite (which I had not seen previously) mentions the possible formation of a black sediment, I quote from p8:

"If a black sediment forms, it is unnecessary to filter, just be careful to take off the necessary amount of solution without disturbing the sediment. If you do not get the desired densities any more, it's time to renew your emulsion."

So, as you have found the sediment does not really matter although it is probably better to leave it in the bottle and just avoid it when you take solution out of your stock. The reason for this advice is "mass action" (a concept from high school chemistry). If the back sediment is in equilibrium with components in the solution, then removing the solid will encourage the formation of more as compared to just leaving the solid in the bottle.

As for other formulations for VDB, I haven't a clue. I don't make a lot of VDB prints but when I do I use the recipe in Christopher James' book which at a quick glance is pretty much what you are using. I've not noticed any precipitate, but I usually make small amounts of sensitizer and do not store it.

glbeas · Jun 8, 2020

Im thinking I need to just make up the component solutions and mix small amounts. The dropper bottle I am using tends to suck up the sludge and it leaves black specks on the paper. I finally got a gradient mask for my images that works and I want to produce a few interesting prints. I also just got a puddle pusher, way easier than a brush, just got to fine tune the coating.

revdoc · Jun 8, 2020

I make up the solutions in separate dropper bottles and mix just before coating. The separate solutions keep very well; only the ferric ammonium citrate is likely to cause problems, in which case, only that part has to be replaced.

nmp · Jun 9, 2020

revdoc said:
I make up the solutions in separate dropper bottles and mix just before coating. The separate solutions keep very well; only the ferric ammonium citrate is likely to cause problems, in which case, only that part has to be replaced.

Curious....how important is it to do the so-called "ripening" of the sensitizer as recommended? Do you still leave the freshly mixed alone for a while before using or do you use it right away as we do in cyanotypes?

koraks · Jun 9, 2020

nmp said:
Curious....how important is it to do the so-called "ripening" of the sensitizer as recommended?

It isn't, despite some people having urged me to accept that really, it is soooo necessary and good prints really cannot be made if the solution is ripened. Turned out to be total codswallop. I make the required volume of solution for a single print by mixing drops of silver nitrate, tartaric acid and ferric ammonium citrate right before coating the paper. It's fast, it's consistent, the solution is always fresh, the performance is excellent. The solution clears immediately upon the addition of the tartaric acid; no ripening is required at all.

Stock solutions of ferric ammonium citrate will grow mold, but it's not a big deal. I just fish it out with a toothpick and keep using the solution; filtering is also an option, but slightly more work.

Oh yes, I did start out doing it the 'official' way, making 50cc or 100cc of Van Dyke sensitizer, only to find that I also had the problem of the silver dropping out of solution, resulting in waste and bringing the risk of unpredictable performance. It's fine if you can use up the sensitizer within a few days or so, but why bother...
It'll probably help to store the ready made sensitizer in a dark/brown bottle, out of any UV light, and if possible with no oxygen. But again, why bother if you can make perfectly fine and predictable fresh sensitizer for each print.

glbeas · Jun 9, 2020

Thank you for your input, going forward this will be my go to procedures. I need to get way getter with my coating rod too. Today I tried wiping a layer then pulling it back but the second stroke didnt cover evenly. You ever add a bit to the puddle on the return to be sure of coverage?

koraks · Jun 9, 2020

Oh yes. But frankly, with van dyke, I find a decent brush to be a way easier approach than a rod. You seemed to be getting quite good results that way too in your earlier prints.

nmp · Jun 9, 2020

koraks said:
It isn't, despite some people having urged me to accept that really, it is soooo necessary and good prints really cannot be made if the solution is ripened. Turned out to be total codswallop. I make the required volume of solution for a single print by mixing drops of silver nitrate, tartaric acid and ferric ammonium citrate right before coating the paper. It's fast, it's consistent, the solution is always fresh, the performance is excellent. The solution clears immediately upon the addition of the tartaric acid; no ripening is required at all.

Stock solutions of ferric ammonium citrate will grow mold, but it's not a big deal. I just fish it out with a toothpick and keep using the solution; filtering is also an option, but slightly more work.

Oh yes, I did start out doing it the 'official' way, making 50cc or 100cc of Van Dyke sensitizer, only to find that I also had the problem of the silver dropping out of solution, resulting in waste and bringing the risk of unpredictable performance. It's fine if you can use up the sensitizer within a few days or so, but why bother...
It'll probably help to store the ready made sensitizer in a dark/brown bottle, out of any UV light, and if possible with no oxygen. But again, why bother if you can make perfectly fine and predictable fresh sensitizer for each print.

Thanks Koraks for that definitive answer. Many times some of these get perpetuated like urban legends - repeated in books without the authors actually trying themselves.

While we are on the subject, what in your opinion is the role of tartaric acid in VDBs. Christopher James says it is "a chemical often employed to assist in keeping high lights from getting muddy" which again sounds like one of those iffy explanations. The mixing sequence seems to be important too. Does the acid help solubilizing the other two components? Or is it a stabilizer/restrainer for silver nitrate (like using citric acid for salt prints?)

Finally, instead of keeping 3 solutions, why not combine A and B and store that instead. FAC with tartaric acid should have no problem co-existing. Then just mix it with the silver nitrate solution before coating.

:Niranjan.

koraks · Jun 9, 2020

Good points niranjan. Indeed, tartaric acid and FAC could be mixed; I haven't tried it, but I see no problem in it.

As to the role of the tartaric acid: firstly, it helps the silver to go into solution. Without it, you end up with a suspension, which won't coat evenly. Secondly, weak organic acids such as tartaric acid and citric acid generally act as an antifoggant with silver nitrate sensitizers. Without it, you very easily get fogged highlights (and unexposed margins). For the same purpose citrix acid is generally used with salted paper printing.

nmp · Jun 9, 2020

glbeas said:
Thank you for your input, going forward this will be my go to procedures. I need to get way getter with my coating rod too. Today I tried wiping a layer then pulling it back but the second stroke didnt cover evenly. You ever add a bit to the puddle on the return to be sure of coverage?

The best way in my experience to do is to figure out how much quantity it takes to make the intended number of strokes for a particular sensitizer/paper combo (will require some trial and error.) Then simply pour/drop that much quantity across the width of paper at one end and go up and down with the rod. Always use a little more than necessary so at the end of the final stroke, there is still some of the bead left over in front of the rod throughout the width of the paper.

revdoc · Jun 9, 2020

To measure the quantities needed for rod coating, I use a 2.5ml syringe. (You can probably find them online. "Slip tip" is the type you want.) I find the quantity of sensitiser needed is pretty specific, and depends on the paper. Not enough and I get uneven coating; too much and I get blotches and spots, but it's pretty easy to get things calibrated after a few prints.

koraks · Jun 10, 2020

revdoc said:
To measure the quantities needed for rod coating, I use a 2.5ml syringe.

That works, but I personally prefer a simple plastic pipette. They come also in 3ml size and they're very convenient for this! Also, they're very cheap.

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