I get a white or grey precipitate if I mix the silver nitrate with the FAC, which clears when I add the tartaric acid.
That's correct. The white precipitate clears upon adding the acid. If any remains, add a little more tartaric acid.
upon the solution standing
I know many/all(?) recipes for Van Dyke Brown mention that you should mix a certain volume (e.g. 100ml) and then let it 'ripen'. I did a lot of VdB's and found that it works just as well, or perhaps even better, if you just mix only what you need on a per-print basis. I.e., the solution doesn't have to ripen, and you don't have to run the risk of the solution somehow going bad/throwing down a precipitate etc. Mind you, I did initially do it 'by the books' and found that the useful lifetime of the solution was way shorter than advertised and that most of the silver over time precipitated out in the form of black nanoparticles, rendering the sensitizer weak and ultimately unusable.
Here's a method that works very well for me.
Mix three stock solutions:
1: Silver nitrate at ca. 11%. Use distilled or demineralized water (!!) The solution should be clear as water and entirely transparent; a tiny bit of milkiness or black precipitate is not necessarily a problem (see troubleshooting below).
2: Ammonium ferric citrate at ca. 20%. Any reasonably clean water is OK. The solution should be dark green, but without cloudiness or signs of mold etc fungus etc.
3: Tartaric acid at ca. 8%. Again, any decently clean water will do. The solution should be clear as water.
I like make small amounts and store these solutions in small bottles with pipette dropper caps for easy dispensing.
I prefer using clear glass instead of brown glass because it makes it easier to see if either the silver nitrate has thrown down a precipitate (it should never do this and last forever; troubleshooting is necessary if it does) or the ammonium ferric citrate goes moldy (it does this, which is not a huge issue and usually you can simply scoop out the yucky stuff with a toothpick; if the solution goes brown, it has oxidized and should be discarded).
To make a print, mix the sensitizer immediately before coating. For a 5x7" piece of paper, I usually mix the following, in the listed order:
5 drops of ferric ammonium citrate solution
4 drops of silver nitrate solution
2 drops of tartaric acid solution
Apply with a good quality brush; e.g. a hake brush or a high quality spalter brush. I prefer the synthetic kind. A single coat is sufficient on suitable papers.
Dry as you please; I use a hairdryer so I can print more or less immediately; as soon as the paper is dry to the touch, it can be exposed. Coated paper does not store well; better use as soon as you can and at least on the same day as coating it to prevent fogging and contrast problems.
Scale up the above amounts to coat larger areas or more absorbent papers; YMMV as they say.
The above method has in my opinion a couple of advantages:
* The individual solutions last very long this way. The silver nitrate and tartaric acid solutions have an indefinite lifetime; the ferric ammonium citrate goes bad eventually.
* If any of the solutions happen to give problems, you only need to mix new that single component. You'll notice when mixing the sensitizer and hence, there's no need to discard a larger volume of mixed sensitizer.
* You can use the solutions for other purposes as well. For instance, the 11% silver nitrate works very well in combination with 1.6% sodium chloride and a drop or two of 20% citric acid for salted paper prints. Likewise, the ferric ammonium citrate could be used with an additional, separate potassium ferricyanide solution for classic cyanotypes.
* The sensitizer solution is always fresh and performs perfectly consistently.
Some pointers for troubleshooting:
* When mixing the silver nitrate stock solution, it immediately becomes milky white as the silver nitrate is added to the water: this indicates that the water used isn't pure enough; in particular there are likely chloride ions present in it. Use distilled or demineralized water. A tiny bit of milkiness is not a problem; the precipitate will oxidize on exposure to UV and drop out of solution as a black sediment. Again, a tiny amount of this is OK, but you don't want the solution to be more or less opaque upon mixing. If there's a tiny bit of milkiness, you don't have to wait before using the solution; you can still use it as is, but the solution will clear over the course of a few days usually.
* A white precipitate is thrown down when adding the silver nitrate: This is normal. It should disappear within seconds on adding the tartaric acid and swirling a bit. If some cloudiness remains, add one more drop of tartaric acid.
* A rusty brown precipitate is thrown down when adding the silver nitrate: this indicates that the ferric ammonium citrate solution has gone bad. Discard it and mix new. Store the ferric ammonium citrate in a dark and cool place when not in use.
* The ferric ammonium citrate has cotton-like clouds floating in it, or a layer of mold has grown on top of it: as long as its color hasn't changed, you can just pick (with a toothpick) or filter (with a cotton pad in a funnel) out the mold and keep using the solution. It will perform fine this way. Only if you get a rusty brown precipitate upon mixing with silver nitrate (see above), you need to mix new.
* The prints give poor d-max; i.e. the blacks are more a mid-brown and not really deep chocolaty brown as they should be: the first thing to check is exposure. Increase exposure by half or an entire stop and see if d-max improves. If it does, but the highlights become too dark, see below for contrast problems. If the d-max does not improve, this usually signifies a problem with the paper. Try a different paper; I find that smooth-surfaced, hot-pressed etching papers work well for Van Dyke Brown. Very absorbent papers tend to give poorer d-max (and they are much more difficult to fix out), and papers with certain kinds of sizing don't interact well with the sensitizer, reducing d-max. Sometimes increasing the tartaric acid compound of the mix helps a bit; try adding another drop of this solution. Don't overdo it; the prints will become grainy and ultimately d-max will actually reduce as you add more and more tartaric acid.
* The prints have streaks: usually a problem with the brush or brushing technique. Invest in a decent brush, and work on technique; this sensitizer is relatively easy to apply evenly, but a minimum of technique is of course required.
* Paper fibers detach from the paper surface as the sensitizer is brushed and/or there are clear fibers visible at the surface of the print on close inspection with a loupe: usually the combination of brushing too long or with too much force (or with too coarse a brush) and a paper with a delicate surface (e.g. Japanse Gampi paper etc.) Try a softer brush, apply less force, and/or use a more sturdy paper.
* The prints have a blotchy appearance with spots or other artifacts: probably a paper problem, particularly related to sizing. Try a different paper; cheaper papers sometimes wet unevenly, resulting in density differences.
* The prints come out way too dark: keep in mind Van Dyke Brown behaves as halfway print-out process, halfway develop-out process. By this, I mean that the printed out image immediately after exposure tends to be on the weak side with only the shadows and lower highlights clearly visible; the higher tones develop out in the first water bath. If you expose long enough to get a printed out image that looks good, the print will turn much too dark in further processing. Reduce exposure by a stop or so and see if the situation improves. If you run into contrast problems by doing so, see below.
* The prints come out way too light: insufficient exposure; try exposing a little longer. The printed out image before it goes into the first water bath should clearly show the deepest shadows and lower midtones (although it depends a bit on paper and moisture content).
* The prints have fogged whites: in any case, mask the borders of the image (use e.g. rubylith, or even a mask cut from heavy-duty tinfoil) so that you can easily see if your whites clear well. If they don't, try a more effective initial wash (I use two changes of water with a pinch of citric acid, 2 minutes each, with agitation), fix a little more thoroughly (increase fixer concentration or extend fixing time) or try a different paper (absorbent papers are difficult to fix). Of course ensure that the work area where you coat and dry the paper do not receive any UV exposure as this will evidently fog your prints.
* The contrast is too low; i.e. the highlights get too dark when the blacks are good, or the blacks aren't dense enough while the highlights are good: use a better negative! While Van Dyke Brown does not require the kind of 'bullet proof' negatives e.g. salted paper does, it still requires negatives with a lot of punch. Usually a negative that prints OK on about grade 1.5 with VC paper should do OK for Van Dyke. Negatives with less contrast will ALWAYS produce compromised prints. If you insist on working with poor negatives, try adding one drop of a
very weak (e.g. 0.25%) dichromate solution to the sensitizer, or a few drops of the same to the wash water. However, I find that dichromate, while boosting contrast, will always affect image tone (it becomes more reddish) and more importantly d-max (reducing it), so it's a compromise, and evidently a toxic one at that.
* Contrast is too high; i.e. either the shadows of the print fall into a black abyss while the highlights are still blown out: negative too contrasty. You're pretty much out of luck here, but I'd recommend looking into salted paper prints, carbon transfer or New Cyanotype.
* There's a lack of fine details in the prints, or they look a little fuzzy: ensure good contact between the emulsion layer of the negative and the print. Also, papers with a coarse surface texture don't render as fine details as smooth papers, so try a different paper. If you really want to stick with a somewhat coarse paper (e.g. a somewhat rough watercolor artist paper), be sure to use a collimated light source; e.g. a single UV LED flood light at a distance from the print or the sun, and not a back of UV tubes close to the print/frame. The use of a collimated light source will improve detail rendering in situations where perfect contact between negative and print surface isn't possible for instance due to small 'valleys' in the paper surface (some art papers).
There's probably more to be said, but this is what I can produce off the bat from my own experiences with this process.
All considered I have to say I prefer salted paper prints because they have a smoother tonal scale. Van Dyke Brown produces a very pronounced S-curve, and that means that in the negatives you need quite a lot of contrast in the shadows in order to get good shadow differentiation in the print. Sometimes this 'harsh' look works well, for graphic-style images, but not all subjects benefit from it IMO. On the other hand, Van Dyke Brown is much easier than salted paper as the sensitizer is easier to apply with good evenness, and exposure times are also relatively short.
Toning can of course be undertaken; gold toning works particularly well. I also tried selenium toning in the past, with off the shelf selenium toner, but found that it severely degraded the density of the prints. Perhaps a self-mixed selenium toner of neutral pH might work, but I never bothered trying it, since gold toning gives (IMO) a much more satisfying end result.
Have fun and be sure to show your prints
