From: Christina Z. Anderson (zphoto@montana.net)
Date: 07/23/02-09:50:23 PM Z
Thanks Richard, Philippe, and Charlie! This is exactly what I was
looking for. I had no idea that the section numbers would be different from
edition to edition. Richard, you are right; I have the Focal Press edition
from 1971 (or at least the library in MT where I xeroxed had that edition).
There have been a couple times I have struggled to find things in Clerc and
now I know why. It makes sense, I suppose, if he were to delete different
processes and add others, the numbers would be different.
There are a couple of us trying to test some of these ideas out of
Clerc, Glafkides, etc. I probably should just break down and buy my own
Clerc.
Chris
Chris,
I found what you asked for in the 1970 Revised edition. Here is what
#687 says:
687. Heavy Intensification with Copper and Silver. A method which has been
used for a very long time, consists in treating the negative in a solution
of cupric bromide in which the silver is converted into bromide and at the
same time fixes an equivalent amount of cuprous bromide.
The negative, after rinsing, is transferred to a solution of silver
nitrate, some of which is reduced metallic silver by the bromide; this
silver is thus precipated with an equivalent amount silver bromide in the
image along with the existing silver bromide according to the following
equations:
Ag+ CuBr2 -> AgBr+ CuBr
CuBr+ 2AgNo3 -> Cu(No3)2 + Ag + AgBr
After washing, and reducing the silver bromide, the amount of silver is
exactly three times that originally present(W.deAbney, 1877). During
washing, the cuprous bromide is partially redissolved or re-oxidized and so
escapes reaction.
The method has been improved by Luther and Schreiber (1923), and by
G. Zelger (1924), by using in the first operation a solution which deposits
in the image not cuprous bromide but a cuprous salt which is absolutely
insoluble and non-oxidizable, such as cuprous thiocyanate or cuprous iodide.
As before, the density is exactly trebled by intensification; it may
be trebled again by repeating the process, and thus sufficient contrast may
be obtained to print an image which exists as a mere ghost, as is sometimes
obtained with films in which regression of the latent image has occurred.
Care must be taken to avoid uneven action or reticulation of the
gelatine if the process is repeated more than once.
The "bleaching" bath(which, as a matterof fact, gives a yellow
image)is prepared by pouring solution (A) into solution(B)-
Solution A
Copper sulphate, cryst. 5 g
Acetic acid, glacial 28 ml
Water to 500 ml
Solution B
Potassium Iodide 5 g
Ammonia 0.880 50 ml
Water to 500 ml
Heat is generated when the solutions are mixed, and the bath must not be
used until cool.The mixed solution, which is clear blue in colour, should be
slightly acid; if it is not, a little acetic acid must be added until blue
litmus paper is faintly reddened by it. This solution is quite stable and
may be used until exhausted.
The negative is immersed in it until the image becomes yellow
throughout its thickness. After thorough washing it is blackened in a
solution containing 0.25 per cent of silver nitrate to which about 1 per
cent of sodium acetate has been added (so preventing the copper nitrate
formed during the reaction from attacking the silver).Before treatment with
the silver nitrate, the negative may be immersed in a saturated solution of
alum, so preventing combination silver nitrate with the gelatine.
The silver salts, other than silver iodide (chloride precipitated in
the gelatine due to the use of ordinary water and silver nitrate combined
with the gelatine), are removed by immersion for about two minutes in a
bath containing about 1 per cent of ammonia, which has no action on the
silver iodide.
The process is completed by reducing the silver iodide to the
metallic state by means of a solution of sodium hydrosulphite containing a
little sodium bisulphite, or by meansof an amidol developer made alkaline
with sodium carbonate.
Hope this what you were looking for.
Cheers,
Charlie
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