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Re: What is a Van Dyke? Kallitype?
There are three iron/silver based printing processes Van Dyke aka Brown
print, Kallitype and Argyrotype. They can be differentiated by the choice
of the iron sensitiser that is used in each particular formula. Van Dyke
uses ammonium ferric citrate, Kallitype uses ferric oxalate and Argyrotype
uses ammonium ferric oxalate.
Both Van Dyke and Argyrotype are 'printing out' processes in which the
image appears during exposure to u.v. light. Kallitype is a develop-out
process in which a latent image is formed during exposure and the reduction
of the silver takes place in a developer.
Van Dyke uses silver nitrate as the silver salt (though I suspect that this
is converted into either silver tartrate or silver citrate depending upon
whether you use citric or tartaric acid in the formula). Kallitype uses
either silver nitrate or silver chloride and Argyrotype uses silver oxide.
The question of permanence depends on the efficient removal of any excess
ferric or ferrous salts plus the removal of thiosulphate (fixer) from the
fibres of the paper. As many have already stated, the 'fineness' of the
silver which is trapped with in the surface layer of the cellulose paper
does leave it vunerable to sources of external pollution.
Are V.D.B. more permanent than salt prints? Well Mike Ware has done a lot
of research into the permanence of salt prints so he's probably the guy to
ask. Check out his web site for further details of the iron based silver
Cheers ...... Tony McLean.
Why not take a look at the latest issue of Camera & Darkroom magazine?