Re: Vandyke Question
Judy and all,
My only "expertise" in VDB is from mixing it in my own studio & observing all those space cadet undergrads have at it... The only failures we experienced were easily diagnosed: in one case a metal cover on one jar of solution (whichever it was) was an obvious contaminant, in the other (as noted) the supposedly distilled water (sealed in an "official" distilled label) turned out to be regular tap water. But beyond that we stirred fast or slow, & probably committed a dozen other breaches without trouble, tho come to think of it I got a call from the department last semester about some VDB trouble (which I think was ultimately traced to contaminated silver jar, but I'll see if I can check back on that).
I know what you mean. I teach Photography I & II for the Continuing Education Department at Prince George's Community College here in Maryland. Trying to get students to do anything consistantly is enough to raise your blood pressure. Some students think all you need to do is agitate film however or slip the paper in the developer and pull it out after a few minutes and you'll have a masterpiece. We had a problem last year where a group of students processed about 20 rolls of film only to get completely blank strips. Turns out that someone in the class before had "spilled" the developer concentrate and replaced it with fixer concentrate so no one would know.
But, given the far better care you have obviously exercised, my guess would be that there's another factor at work, that for instance one of your chemicals could be below par. Have you made the emulsion from these chemicals successfully, or with less hassle, in the past?
I wouldn't call my working habits "meticulous" but I do clean all equipment with soapy water after each session. All chemicals are stored in glass containers with plastic caps, measured into condiment cups which are discarded after use, and the measuring spoons are cleaned between each chemical. The silver nitrate and tartaric acid were purchased from photographers' formulary in 2002 and show no signs of contamination. The FeAmCitrate for the original (2 year old) vandyke sensitizer was purchased at the same time from photographers' formulary. I wanted to make traditional cyanotype sensitizer in January of 2007 and found black flakes throughout the FeAmCitrate so I bought a pound from artcraft and had no problem. When I tried to make the new vandyke sensitizer about 2 weeks ago and ran into the precipitate. I ordered new FeAmCitrate, tartaric acid, and silver nitrate from artcraft and got the same problem. Thinking it might be the distilled water I bought some from the local food store; to no avail. I am stumped though I am beginning to wonder if the FeAmCitrate is the problem since the amount of precipitate filtered is in line with the volume of FeAmCitrate I measured out. I'll order a batch from photographers' formulary and see if that cures the problem.
Alberto Novo brought up a good point with the possibility of there being an excess of FeAmCitrate, so I checked the calibration of my scale which measures to 0.01 gm and it is off by about 0.02 gm; not enough to cause this kind of problem.
My only other comment at this point is that I, too, have used VDB emulsion more than a year old without a problem. The inside of the jar seems to plate with silver fairly soon, without any noticeable effect on the print, and old emulsion will have black specks which reabsorb as soon as the solution is smoothed on the paper.
I tried both the old and new sensitizers and I had to double coat the paper to get the density I wanted but in the end everything worked out just fine.
Best to all, Scott