Mysteries Of The Vortex (Part One)

Conclusion – for now...

Reducing residual thiosulphate levels is the main purpose of print washing and still the leading known predictor of print LE. Many authorities agree that a standard of zero visible staining using full sheet tests of HT-2 is a fully effective practical test for residual thiosulphate levels. See end of article for the formula and testing procedures for using HT-2. The second half of this article “Mysteries of the Vortex Part 2: Archival Washers in Practice” will detail specific tests performed on one make of washer – tests designed not only to prove the effectiveness of the washer, but to support or disprove various ideas and hypothesis about print washing in general. Part 2 will suggest design considerations for a hypothetical “ideal” print washer, and conclude with a number of specific recommendations you should consider adopting in your own darkroom.

Kodak HT-2 Residual Hypo Test  (Published by David Vestal in 1996)    

  Formula:

      Water               375ml
      Acetic acid 28%     62.5ml
      Silver nitrate      3.75 grams
      Add water to make   500ml

Put 50 to 100 ml of this solution in a small brown glass bottle with a
dropper cap. Keep the rest in a sealed brown glass bottle. Keep it 
cool and in the dark. Don’t touch it or drink it: it’s poisonous and it 
leaves permanent stains.

To use HT-2: Develop and fix an unexposed sheet of the paper you
  are printing on; put it through exactly the same processing as your 
prints, including washing aid treatment and toning. 
  
At timed intervals during the print wash, pull this test sheet out of 
the wash, cut off a small sample, an inch square will do, and put the 
rest of the sheet back in the wash. Blot all surface water drops off 
the emulsion side of the sample with a paper towel, and then put one 
drop of HT-2 solution on it. Leave it for exactly two minutes then rinse 
off the HT-2 drop with cold water, blot the sample with paper towel 
and examine the stain immediately (it will soon darken). 

Do this in dim white light. A definite brown or deep yellow stain shows 
that the wash is far from finished. A light beige stain means you’re 
getting somewhere but have not arrived. When there is no stain at all, 
or a yellow stain so pale that it seems no darker than the paper 
(some papers seem never to get to no stain), the wash is at least fair 
and may be excellent. Then it’s not bad to wash for another half hour 
for luck. The distribution of hypo in the paper can be uneven, so 
although a definite stain always means too much hypo, a very light 
one doesn’t always mean there isn’t too much hypo an inch or two 
away from the test spot. 

If your prints still look new after 200 years, your fixing toning and 
washing were probably good. 

[n.b. a ready-made HT-2 kit comprising solution + colour test-card 
is available from Silverprint]