Residual Hypo test

[Lee Shively]

In the past, I would test for residual hypo on a reject print that I would toss out after testing. Today, I tested a keeper print. I squeegeed the surface dry and placed a drop in one corner, waited two minutes and blotted off the solution. I got no stain so I thought everything is fine. Now the print is dry and there's a faint tan stain where the solution was placed.

My procedure is to use a two rapid fixer bath for 30 seconds each, holding tray with a weak solution of a washing aid, rinse in a large tray for a few minutes, HCA for ten minutes with regular agitation and shuffling of prints and 60 minutes in a Versalab washer. Now I'm worried that I'm not washing enough. Any suggestions?

 

[photomc]

Lee, I would not worry..or maybe I should. My understanding of the residual hypo test is that is to be read after a couple of minutes and then checked. Afterwards a slight stain will occur and after a few days it may be quite a bit darker. That's why I DO NOT use it on a print I plan to frame or keep.

Be interested to hear from others here.

 

[dancqu]

I thought at one time the silver nitrate in the test solution to be
printing out. Maybe not. Although the halides of silver are by light
reduced to silver, that is likely not the case with the nitrate. Of
course as soon as that nitrate hits all that organic matter ... .

Nitrate is a strong oxydizer and may be "burning", coloring, some
portion of the gelatin.

If there is any hypo remaining then the acetic acid in the test
solution decomposes the thiosulfate present leaveing free sulfur
which combines with silver giveing a stain.