Voila la réponse de Richard. J'avais compris qu'il avait été employé de Kodak mais ce n'est pas le cas.
I should make clear that I was never employed by Kodak nor have I taken part in any research on washing. I did write a couple of summaries of generally available information on the subject.
FWIW, an enormous amount of research has been done on both fixing and washing over nearly a century. Much of this work was done by Kodak Research Laboratories and published in various scientific and technical journals. The criteria for "archival" or long image life washing of silver prints was amended significantly following the discovery by T.H.James, of Kodak, and another researcher at Fuji, that very small amounts of hypo retained in the emulsion actually protected the image from attach by peroxides. As a result the previous recommendations for very long washes were changed.
The washing process for the _emulsion_ appears to be a diffusion process but for unprotected paper support it is partly diffusion and partly frictional because the hypo is held in the fibrous structure of the paper. It was to avoid this that Ilford came up with their "archival" processing method which uses very short fixing times. The Ilford process does not work on all paper; some will just not fix out quickly enough. However, other research shows that conventional processing, especially when a sulfite wash aid is used, results in washing down to archival levels with relatively short washes.
The frictional effects of the support and also the adsorption of hypo and reaction products by the Baryta layer, account for the longer washing times required for "fiber" paper. According to Dave Valvo, a former product designer for Kodak, the longer fixing times required by fiber base paper in comparison to RC is due to penetration of some halide into the Baryta layer, this also results in extended washing times.
Kodak research of about the middle to late 1930s was very thorough; they measured the absorption of hypo in uncoated paper, paper with only the Baryta layer, emulsion alone and various combinations.
I don't know what Ctein did but it was probably re-inventing the wheel.
A note: for best permanence the image must be toned in either a sulfiding toner or a gold toner. Selenium toner also provides complete protection if carried out long enough to tone all densities.
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Richard Knoppow
Los Angeles
WB6KBL
dickburk@ix.netcom.com
www.danielbouzard.com