[Alt-photo] Test for residual hypo in salt prints
marekmatusz at hotmail.com
Sun Aug 13 00:56:01 UTC 2017
I am definitely looking at the simple silver nitrate test and actually no stain at all. Zero change from the plain paper control. So not even the slightest yellow. Now all my salt prints are gold toned. If you are not gold toning than some residual thiosulfate might actually be beneficial.
Sent from my iPhone
> On Aug 9, 2017, at 6:39 PM, Ryuji Suzuki via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
> For practical purposes and troubleshooting, I recommend the simple silver nitrate test and don't bother with methylene blue test.
> Silver nitrate test is easy and sensitive enough for practical purposes. If you see anything more than pale yellow, revise the washing process. Static soak is not efficient, however long. Slow flow of fresh water is wasteful. Reasonably vigorous agitation with a few changes of water is probably most effective.
> Residual thiosulfate does not stay in the same chemical form over time in the print, but it slowly degrades to products including harmful active sulfur compounds. Methylene blue test doesn't pick up the latter, so it is only useful for laboratory testing of freshly prepared test specimen. The sensitivity and quantitative measurability is better, but these advantages are of little practical impact.
> Ryuji Suzuki
> "Don't play what's there, play what's not there" (Miles Davis)
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