The recent thread on Toning and Permanence (thanks to Paul R for the initial post!) identified Christopher Gmuender's 1992 RIT master's thesis as a key source of experimental data on the effect of toning on paper. So I ordered a copy from the RIT library, to see for myself what it had to say.
Gmuender applied three different "stress tests" to each of eight different papers treated with varying dilutions of 7 different post-treatments - a monumental job. The bulk of the thesis is close to 350 pages of tables and graphs of densitometer readings. I've sifted through enough of it now to have some degree of comfort in interpreting the summary conclusions earlier in the document.
The tests were extended fuming at high temperature with hydrogen peroxide, treatment with Kodak's TC-1 potassium dichromate bleach formula (otherwise intended as a highly corrosive tray cleaner), and incubation at high temperature (50C)/high humidity(80%RH).
The papers tested, all in glossy surface, were:
Agfa Multicontrast RC
Kodak Polyconstrast III RC
Ilford Multigrade III RC (whether it was the Deluxe or Rapid version was not specified)
Oriental VC RC (I assume this was the paper that Oriental calls "VC-RP")
Agfa Brovira DW grade 2
Kodak Elite DW grade 2
Ilford Galerie DW grade 2
Oriental Seagull DW grade 2
Seven of these papers were discontinued long ago. I believe the Oriental VC RC paper is still available, though I do not know whether it's the same formulation as was available 13-14 years ago.
Post-treatments tested were:
IPI J-Toner (described as similar to Kodak Brown Toner) at various dilutions
Kodak Polytoner (proprietary formula, no longer available) at various dilutions
Kodak Rapid Selenium Toner at various dilutions
Kodak Sepia Toner
Kodak GP-1 Gold Toner
Kodak GP-2 Gold Toner
Note that the temperature for all toning treatments was 25C/80F, which is considerably higher than most of us use. Toning time was 3 minutes for J-Toner, Polytoner, Rapid Selenium Toner and Sistan, 5 minutes for the gold toners, and followed the recommended bleach/redevelopment cycle for Kodak Sepia Toner.
The resulting data are fairly messy in detail. Given the huge number of combinations, Gmuender was able to do only one run of each. The resulting statistical anomalies make it inadvisable to try to read very much into the fine detail of each individual test. Also, the papers varied somewhat idiosyncratically in their behavior, underlining the difficulty of extrapolating the detailed behavior of these mostly discontinued papers to specific products available today. However, there were some reasonably clear overall trends. Some things that caught my attention, in no particular order:
* Sistan had no apparent protective effect in these tests.
* The sulfiding toners, in general, offered good protection.
* Selenium toner at 1:4 and 1:10 dilutions offered good protection.
* The gold toners offered less protection than selenium or the sulfiding toners; GP-2 was more effective than GP-1.
* With selenium toning in particular, RC papers toned more readily and achieved higher levels of protection than did FB papers at a given dilution. RC papers were able to achieve a good level of protection at 1:25 dilution, while FB papers needed 1:10. However, at 1:10, FB papers also achieved a good level of protection.
The problem with these data is that, at least with respect to selenium, they don't directly address the question that most users will have: does toning at 1:20 or 1:40 for ten minutes or so at 20C/68F have a worthwhile protective effect? Unfortunately, for reasons that are not obvious to me, and are not explained in the thesis, Gmuender chose 3 minutes at 25C/80F, and there's nothing in his data that enables us to quantify the effect of simultanously reducing the temperature, increasing the dilution and extending the time. Strictly speaking, taken alone, the results reported in this thesis give no conclusive guidance as to how to extrapolate the results to more typical working conditions, and thus what toners we can use to assure a good protective effect under usual conditions.
His results leave other open questions, too.
I'm intrigued by the total absence of benefit from Sistan in the face of these particular environmental insults. I'm also intrigued by the surprisingly favorable results with the RC papers, especially with selenium, which is so easy to use. I wonder whether the high degree of protection achieved against oxidative attack, especially in the very aggressive dichromate bleach test, suggests that heavy toning will be enough to squelch over the long run the light-driven, titanium-dioxide-catalyzed deterioration sometimes observed in RC papers, as was observed in the short run with light toning (and with Sistan!) in Ctein's test.
Anyway, there you have it. There are probably other insights to be gained if I can find the time to mine the data more intensively. I don't know when or whether I'll get to that, but in the meantime, if anyone here has any specific questions about what I've reported, I'll try to answer them as best I can.