U of S | Mailing List Archive | alt-photo-process-l | Re: Kodak HT-2 residual hypo test

Re: Kodak HT-2 residual hypo test

----- Original Message ----- From: "Judy Seigel" <jseigel@panix.com>
To: <alt-photo-process-l@usask.ca>
Sent: Monday, August 11, 2008 7:35 PM
Subject: Kodak HT-2 residual hypo test

To make 1/2 liter of Kodak HT-2

water ------ 375 ml
acetic acid (28%) ---62.5 ml
silver nitrate  ---- 3.75 g
water to make 500 ml

My only comment is to mix this with distilled water which is free of chlorine. Chlorine will react with the silver nitrate to form some silver chloride. The mixture should be clear after mixing. Cloudiness indicates some inpurity has reacted with the silver to form a compound.
The Kodak formula is for 1.0 liter, too much. Kodak recommends allowing the test solution to stand for 2 minutes before rinsing and blotting it off. Film should be held against a white paper background to increase the visibility of any stain. Kodak gives the life of the test solution as 6 months. Avoid exposure to light.
At one time Kodak published a comparison chart with color chips to use with this test in estimating the amount of residual hypo. The more elaborate version of the test I mentioned fixes the stain so it does not darken with time and can be used for quantitative measurements using a densitometer to compare it with stains produced by known amounts of thiosulfate. A three step chart is published in many editions of the _Kodak Black-and-White Darkroom Dataguide_.
While this is not the most sensitive test it is sensitive enough to indicate adequate washing for permanence. Vestal was wrong about the lack of a standard, there are standards for maximum thiosulfate content for long life. Again, later research showed the undesirability of washing out every trace of thiosulfate especially where the image is not toned. Where images are toned the main criteria seems to be to get it clean enough not to affect the toning process. Washing conventional films and prints according to the instructions given by Kodak for Kodak Hypo Clearing Agent will suffice.
Because of the importance of permanence in photographic records of various sorts a very great deal of research has been conducted over a period of a century or more. AFAIK, very little research has been done on the conditions for permanence of alternative processes although some of that applying to silver-gelatin materials _may_ also apply to other processes where the iamge is composed of silver since the silver will probably be similarly vulnerable to oxidation and uncontroled sulfiding.

Note that Kodak states that there is no simple test for the amount of silver in a fixing bath, its better to test for residual silver in the fixed materials.
I will add the formula for the residual silver test for completeness of fixing:

Kodak ST-1 Stock Solution

Water 100.0 ml
Sodium sulfide, anhydrous 2.0 grams
Store in a small, stoppered bottle for no more than three months.

To use dilute the stock solution 1 part stock to 9 parts water. Working solution should be replaced after a week.
Place a drop of the working solution on a clear part of the image and allow to stand for about 3 minutes. Then rinse and blot off. Any staining other than a very faint yellowish stain indicates too much silver and the material should be re-fixed.
At one time Kodak also recommended a 1:9 dilution of Kodak Rapid Selenium Toner as the test solution. This is relatively odor free and is long lived, however, it fails where there is an excess of hypo in the print or film.

Although this may all seem off topic for an alternative processes list I remind you that the majority of original images used in alt printing are on conventional silver-gelatin film and most photographers/artists would consider its permanence of some importance.

Richard Knoppow
Los Angeles, CA, USA