Auteur: Christophe Frot
Date: 16-06-2006 19:55
Gilles,
Pas de probleme!
Le virage au Pt est un des nombreux virages aux metaux precieux disponibles et developpe depuis plus d'un siecle... on en a discute sur l'ancien forum (je te laisse explorer les archives!). C'est bien evidement different du tirage au platine (ou au palladium).
Je cite Daniel Bouzard :
"A ma connaissance avec les papiers modernes chloro bromures le platine
n'a pas d'interet pour les virages platines . A conserver pour virer des papiers
salés ou Kallotype ou Van Dick ..... "
Si tu veux, voici quelques formules et un texte...:
http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00Cept
http://albumen.stanford.edu/library/monographs/reilly/chap8.html
http://www.barryleighton.com/Formulaepages/Platinum%20toner.html
http://www.usask.ca/lists/alt-photo-process/2001/sept01/0188.htm
http://www.cjballphotography.org.uk/formulae15.html
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THE PRACTICE OF PLATINUM TONING
The effects obtainable with platinum toning do seem to harmonize
especially well with a matte surface, although platinum toning can be
used with albumen and other kinds of glossy paper. The main technical
difference between gold and platinum toning is that gold toning goes on
best in an alkaline environment, while platinum toning requires a
neutral or acidic condition. One difficulty in platinum toning is the
tendency to produce yellowish highlights if the toning is carried on
too long, or if the solution is too strong or too acidic. Another is
the tendency of any impurities such as silver nitrate or sodium
thiosulfate to rob the toning bath of its activity by altering the
platinum to an irreducible condition. For this reason prints to be
toned in a platinum toner must be well washed and treated in a 5%
sodium chloride solution for 2 minutes and then washed again for 5
minutes in running water before being placed in the toning solution.
Still another precaution to be observed is to wash the prints well
after toning, to be sure that none of the acidic platinum toner is
carried into the fixing bath.
A useful platinum toning formula is as follows:
Potassium chloroplatinite, 1% sol 50 ml
Citric acid 4 g
Water 750 ml
Combined gold and platinum toning may be used to obtain neutral blacks;
tone the prints in the Borax gold bath until they are lilac in color,
and long enough in the platinum toner to achieve a neutral color. It is
not possible to consistently attain the absolutely neutral black
characteristic of the platinum print itself, however.
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@+
Christophe
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