Re: Merits and Demerits of Salted vs. VDB
I think the public would be hard pressed to tell the difference between the two in a finished print but salt has traditionally been called the poor man's platinum because of its very long tonal range. On Weston paper the VDB and salt look very similar tonally, to me, with about the same amount of stops, but generally you have to use a flatter neg with VDB than with salt. If you match the neg to each process with a digital curve and digital negatives, I think it would be hard to tell the difference even more.
There are 6 processes I teach in my alt class--first cyanotype to learn the digineg process, then we move to VDB and argyrotype, then gum, then pt/pd and then salt. This past year I eliminated argyrotype and made salt optional though I demoed it, because all three are essentially brownprint processes and it wasn't really necessary to have them do all three.
However, in my packet of step wedges and test prints and tonal palettes printed in both, I notice that there is a fading and yellowing and mottling in the VDB packet I do not see in salt. The salt prints look exactly like they did the day I made them. In the troubleshooting section of my VDB chapter (Alt Proc Condensed) I have a quote from Mike Ware via Wynn White: "Most sources state that Vandyke prints can be cleared in plain water. In Mike Ware's description of the argyrotype process he explains the problems iron-based silver processes have. If processed in an alkaline solution residual ferric iron is left in the print which will eventually cause it to fade since iron (III) will oxidize silver."
With test strips and wedges since I am only using them to scan and read data, I am not as careful in my washing/fixing. Thus these WOULD be more prone to showing incorrect processing, which they do. BUT, where VDB uses iron in the mix, salt does not--salt is a silver/chloride process and VDB is a silver/iron process in other words. Hence, this could be one reason to prefer salt. If you are careful with your processing and use citric acid in your wash baths for VDB so the pH is below 7, Ware says this should solve that problem.
If a salt print looks gross as Sandy says it is a fogging that occurs immediately. This is due (if there is no undue light exposure) to a paper without enough sizing so that the solution sinks too far into the paper. Buxton, a great paper for cyanotype, looked terrible with salt when I used it. BUT the other thing not enough sizing does is not provide enough organic compounds in excess for the whole process to occur. If organics are not in excess proportion to the silver you get a dull grey print. The active organic substances in some way facilitate the reduction of silver chloride. Ryuji could explain why this is so, I have no idea.
One more thing you can do with salt--vary the color of the print from sepia to red brown depending on your salt form--ammonium chloride is more red brown. You can tone both processes.
VDB is such a quick, easy process, not requiring the two step size and then sensitize that salt does. But if I were to choose one over the other I would choose salt. But in a classroom, VDB is way easier to teach and students tend to be more successful with it.
This is obviously way more than you need to know but you asked...
From: "Ross Chambers" <email@example.com>
Sent: Saturday, September 01, 2007 2:06 AM
Subject: Merits and Demerits of Salted vs. VDB
To the brown folk,