From: Richard Morris (Richard.Morris@brunel.ac.uk)
Date: 02/12/02-02:42:09 AM Z
Firstly wet and dry plates ain't calotypes!! These are images made on paper
negatives to Talbot's discovery of 1840.
That said the fastest known calotype exposure was 1 second about 1852 by
Nicholas Henneman. I forget, without looking up my files as I am
not replying from home, if it was an image of a girl or a Hungarian, said
to be Kossuth. One was three seconds and the other one. I have seen both
images and a letter from Talbot sending them to John Dillwyn Llewelyn.
Malone was said to be experimenting with some French paper, which may have
given faster exposures, and we don't know what lens Henneman used either.
On average 2 minutes at f8 was quite reasonable. I have done one in 3
seconds using Talbot's portrait camera with a lens of around f1.6 but it
wasn't very good!
Calotypists also used to play around with the proportions of chemicals
depending on whether they were using the paper immediately or later. More
gallis acid preserved the paper but apparently reduced the sensitivity. I
feel that it is worth trying different proportions as modern papers don't
have the same properties as Talbot's and probably chemicals are now purer
which may or may not help. I can say that different makes of silver nitrate
do make a difference by wbhy I don't know.
With salt paper, Talbot's original Photogenic Drawing process of 1834/5,
announced in 1839, he used to resensitise the paper several times, until
just before it became darkened spontaniously, and found that way that it
was more rapid. He also, just prior to the discovery of the calotype, used
to add a few drops of gallic acid.
Richard Morris
On Tue, 12 Feb 2002 09:16:35 +0100 (CET) "=?iso-8859-1?q?F.=20Wentzel?="
<fotochemiker@yahoo.de> wrote:
> --- Martin Reis <mreis@tafelmusik.org> schrieb: > Hi
> there,
> >
> > I am somewhat new to the alt processes and wonder if
> > there are any simple
> > ways to speed up salt prints, wet and dry plates
> > (calotypes). Can a chemical
> > be added to
> > speed up sentiziation. That is using that fastest
> > light
> > sources available. Just got my copy of Primitive
> > Photography and the
> > processes described in it seem
> > quite slow.
> >
> > Cheers
> > Martin
>
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Richard Morris
Brunel University, UK
dtsrrlm@brunel.ac.uk
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