[pure-silver] Re: KRST

Wow, thanks for that elaboration & those citations, Richard. As always, I appreciate your time & thoroughness!
In trying to get a handle on all of this, and break it down to the simplest terms so I can remember it well enough to put it into practice, I looked back into my own personal archives of pure-silver posts on this topic. I think I found one which condenses it, in this excerpt from an 11/03 post (AFA I can tell) by Russ Gorman:
Silver sulfide and silver selenide are both very stable compounds, much more stable than metallic silver. Toners which convert some or all of the image silver to these compounds protect the image from further sufiding and from oxidation. These images are very long lived even in hostile environments.
Gold toners are also very effective in protecting the image. They are not much used in general photography due to the high cost.
In the past Kodak Rapid Selenium Toner at a dilution of 1:20 was recommended as a general treatment of prints and films for protective purposes. It was discovered about ten years ago that brief toning at this high dilution was not protecting the low density areas of the image. The effect was discovered in microfilm, which exhibited signs of oxidatative attack .
A greater degree of toning in a less dilute solution (1:9) does provide adequate protection although it causes greater change to the image color or density. Partial toning in a polysulfide toner like Kodak Brown Toner, or Agfa Viradon does tone all densities evenly. Full toning in any sulfide or Selenium toner provides full protection. This includes all direct and indirect (bleach and redevelop) sulfide toners.
Gold toner also provides complete protection provided toning is carried out sufficiently. Gold toner was the standard method of protecting microfilm for decades. Gold is similar to Selenium in that it makes little change in the color of cold or neutral colored images. It produces a bluish color on fine grain images and is useful where one wants a neutral or slightly cold tone.
Not all toners which produce brown tones are suitable for image protection. For instance, Copper toner results in images which are less stable than untreated silver. The useful toners are those which convert part of the silver to silver sulfide, selenide, or gold plate them.
And this interesting note, from Ralph Lambrecht at about the same time (in response to a post from Ryuji, I think):
I gave up mixing KBT and KRST as well. For some reason, I thought the smell was worse than KBT alone. For now, I use KRST first for a minute, followed by KBT for a time depending on desired hue. A minute will not change tones much, two will give a warm light brown, and four minutes of more give a reddish brown in Afga MCP and a significant split-toning effect in Ilford MGIV. The combination toning results into tones and depth of hues, one can't get with either toner alone.
I haven't tried using KBT first followed by KRST and don't know what that would give me or why it would be better or worse for archival purposes. 

# # #
So if anyone wants to vote me in as the pure-silver archivist (or plagiarist for freely copying others' posts, although I am not taking credit), I'll bite. As long as it's for double the salary I'm getting for the job now. 

Adrienne Moumin
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----- Original Message -----


From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: KRST (was Sistan and Senior Moments)
Date: Fri, 17 Aug 2007 11:17:02 -0700

 Not speculation at all but the results of extensive

research by the Image Permamence Institute of the Rochester
Institute of Technology.

 I can't find the citation to the original research on KRST
but its mentioned in a paper describing sulfite wash aids
(1).
     This paper mentions the use of diluted KRST and points
out that even with its use the vulnerability of microfilm to
oxidative attack is greater when it is overwashed. The
effect of overwashing was investigated by the IPI in the
research leading to the report mentioned below, it was not a
factor in the failure of KRST to protect the NEH microfilm
or other microfilm found to have the same problems.

     The RIT research was done for the National Endowment
for the Humanities in 1991, the full title is:
_Final Report to the Office of Preservation National
Endowment for the Humnities
Grant No. PS-20152-57_
_Sulfiding Protection For Silver Images_ James M. Reilly,
Kaspars M. Cupriks, Image Permanence Institute Rochester
Institute of Technology, March 38, 1991

   Reprints are available from the IPI.

     While this paper addresses microfilm and not printing
paper there is enough similarity in the emulsions to think
its valid for paper also. I also had several private
conversations with Dr. Douglas Nishimura, a scientist at IPI
with direct involvement in the research who stated to me
that KRST at 1:19 was NOT completely effective for paper for
the reasons stated for microfilm in the above document.
     A more effective treatment is a Liver of Sulfur type
sepia toner. IPI concocted their own version intended to
have low odor but packaged toners are quite effective. These
include Kodak Brown Toner and Agfa Viridon of the second
type. Kodak published formula T-8 is also effective.
     Kodak has published a paper on the use of KBT for
microfilm protection. It is Publication No. A-1671, _Use of
Kodak Brown Toner to Extend the Life of Microfilm_
available on-line from the Kodak site.

1,  _The Effect of Salt Baths on Hypo and Silver
Elimination_ R. W. Henn, Nancy H. King, J. I. Crabtree,
Kodak Research Laboratories, 1956 "Photographic Engineering,
Vol7, NOs 3&4, p.153ff
     This paper also has a considerable bibliography of
research papers pertaining to fixing and washing.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx


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