[Alt-photo] Test for residual hypo in salt prints
rs at silvergrain.org
Wed Aug 9 23:39:02 UTC 2017
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.
"Don't play what's there, play what's not there" (Miles Davis)
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