From: Richard Sullivan (richsul@earthlink.net)
Date: 01/25/02-02:10:19 PM Z
I am not a real chemist but my understanding is the "toning" process is a
double replacement process. In fact much of the silver is actually replaced
by the platinum rather than just a plating over. Perhaps a real chemist can
illucidate.
--Dick
At 02:41 PM 1/25/2002 -0500, you wrote:
>Peter Marshall wrote:
>
>And if you tone the kallitype with platinum it will become even more
>difficult to tell the difference between the two! In fact, I understand
>that a very expensive testing procedure would be needed to distinguish
>between a full-bloom platinum and a platinum-toned kallitype.
>
>I platinum tone all of my kallitypes, not to fool anybody but because I
>think it greatly adds to their permanence. What I do is develop the
>kallitype in a 20% sodium citrate developer, which gives a warm brown
>image, then tone with the formula Dick gave yesterday (5 g of citric acid
>per liter of water, plus 5ml of platinum #3 solution). This is done after
>clearing but before fixing. Toning is usually a subtle process but with
>this developer/toner combination the result is quite dramatic as the brown
>image rapidly turns to a neutral black on contact with the toner. Less
>rapidly of course as the toner depletes.
>
>As for image permanence, which has always been an issue with the
>kallitype, one could make a good case that a well-processed kallitype,
>platinum toned, is as permanent, if not more so, than any other type of
>silver image. The keys to permanence would seem to be, 1) complete removal
>via clearing of unused iron, 2) proper fixing of the image to remove the
>unused silver, and 3) complete removal of the hypo via adequate washing,
>or its conversion through the use of a hypo eliminator which allows a
>shorter final wash.
>
>Sandy King
>
>
>>
>>I've made prints from the same neg and the only way I could tell which
>>was Pt/Pd and which Kallitype was by looking on the writing on the back. I
>>was using a developing out method with both processes, and there were no
>>significant differences in tonality/tonal range.
>>
>>We have speculated in the past that some 'platinum' prints in collections
>>may actually be kallitypes. There were several formulae published around
>>1900 which claimed to produce kallitypes which looked identical to
>>platinum.
>>
>>Peter Marshall
>>Photography Guide at About http://photography.about.com/
>>email: photography.guide@about.com
>>_________________________________________________________________
>>My London Diary http://mylondondiary.co.uk/
>>London's Industrial Heritage: http://petermarshallphotos.co.uk/
>>The Buildings of London etc: http://londonphotographs.co.uk/
>>and elsewhere......
>
>
>--
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