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Mysteries Of The Vortex (Part One)
Mysteries Of The Vortex (Part One)
Author: Martin Reed (Silverprint)
Published by Les McLean
19th November 2008
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A Practicum On Print Washing


As anyone reading this will be aware, washing black-and-white film and paper after developing and fixing is necessary to remove both unused fixer and complex silver/thiosulphate compounds produced during fixing. It’s easy to regard the washing phase as the tedious postscript to the processing cycle, but perhaps it’s time to review the washing and fixing stage in the light of recent research and, in many geographic areas, the increasingly pressing need for water conservation. Although the nature of fibre base (FB) paper demands higher washing standards than those required for film and RC materials, I believe we tend to grossly over-specify on FB washing and that by controlling factors within the washing and fixing steps we can waste less time and water.


“Archival” standards

The term “archival” applied to photographic prints has been so overused that authorities are now shy of it and the LE (life expectancy) factor is being adopted as an assessment of potential longevity. Aside from deterioration caused by storage and display, the principal factor controlling longevity in fibre based paper is the residual thiosulphate level, expressed in weight relative to unit area. The easiest to comprehend is grams per square meter, but those working in the field think in terms of micrograms per square centimetre (ug/cm2). One microgram is one millionth of a gram. The conversion is simple:


0.01grams per square meter = 1 microgram per square centimetre.


The standards accepted for archival or high LE are not yet fixed but are well defined. Ilford has an in-house standard of 0.7 mg/cm2 but discussion among all manufactures continues; a recommended upper limit of 1.5 to 2 mg/cm2 is likely to be the eventual recommendation for safe storage.

The cornerstone of basic thiosulphate testing in the home darkroom is the HT-2 reagent, which can be used with a Kodak Hypo Estimator to get a reasonable evaluation of thiosulphate content. The HT-2 is not accurate with very low levels of thiosulphate; for those, more complex procedures must be used. Until recently this was the “Methylene Blue” test from the ANSI standard. All the major manufacturers are now using the iodide amylase test, due to be published soon in a new standard.


Definitions

Figure 1 shows the structure of fibre-base paper. While film and RC materials are relatively easy to wash because processing solutions only penetrate the emulsion, the porous base of traditional paper accepts chemicals readily. Washing can be looked upon as three distinct phases that proceed simultaneously:

  1. Salts in the base of the emulsion diffuse towards the surface of the paper.
  2. The salts diffuse into fresh water at the paper surface.
  3. This water then is replaced using agitation and/or water flow.




An interesting hypothetical way of looking at washing is to think of an 8 x 10 print that can, theoretically at least be archivally washed in only 300 ml of water. Assuming a fibre-base paper 0.03cm thick, a print of this size will have a total volume of approximately 15ml. This print, removed from the fixer is permeated by thiosulphate throughout the base, baryta and emulsion layers. With a 15 ml dose of fresh water, and sufficient time for the thiosulphate content in the print and fresh water to equalise, the thiosulphate content has been reduced to half its initial level with this single washing step – using a minimal amount of water. Repeating this process ten times reduces the hypo level to one thousandth of its initial value; repeating it 20 times will reduce it to one millionth. All using only 300 ml of water! This dramatically illustrates that the exchange of water is a significant factor in washing.

However, this approach might take a long time. This hypothetical model ignores the influences of agitation quality, which may vary considerably; the effect of washing in an enclosed tank of continuously running water; the retarding of the process by slow diffusion of hypo through the paper structure; and the problem of paper retained by the paper structure. How, then, can this idealised approach be most closely met in practice?

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  #1  
By Mike O'Pray on 20th November 2008, 12:40 AM
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Many thanks for this Les. Now it's set out and easily accessible.

Mike
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  #2  
By Argentum on 20th November 2008, 10:44 AM
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Thanks for that Les, I've snaffled it and converted into pdf for local reference.
Now if part 2 was only in text format instead of scanned magazine pages I could do the same but with a much smaller file size.
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  #3  
By Ag-Bromide on 21st November 2008, 08:57 PM
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I hope Martin Reed makes it available as a PDF for downloading (unless I`ve missed it on Silverprint`s site).
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  #4  
By Argentum on 21st November 2008, 09:13 PM
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Part 2 is available from the web site but its scanned pages from a magazine which makes it 16MB.

http://www.silverprint.co.uk/pdf.asp

mysteries of the vortex part 2
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  #5  
By Dave miller on 21st November 2008, 09:41 PM
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We will be posting part two here shortly.
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  #6  
By Andrew Bartram on 26th November 2008, 08:56 PM
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What a fantastic resourse this User Group is! I have long mourned the demise of "Darkroom User" Magazine and regularly re-read the original "Silverprint Manual" that went on to be the original AG+ Periodical (now sadly too much devoted to digi stuff I don't want to think about).
Some of the above was indeed published in the Silverprint manual.
Thanks Les for making it available
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  #7  
By Martin Aislabie on 9th December 2008, 01:46 PM
Thumbs up FB Washing Explained

What a well argued piece of work, with some back-up data to support his case.

So often these articles are a mixture of old wives tales and opinioneering.

Thanks for posting it Les

The only thing that puzzles me - why Martin doesn't have this article on his web site along side Part2 ?

Martin
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  #8  
By Les McLean on 9th December 2008, 03:19 PM
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Quote:
Originally Posted by Martin Aislabie View Post
What a well argued piece of work, with some back-up data to support his case.

So often these articles are a mixture of old wives tales and opinioneering.

Thanks for posting it Les

The only thing that puzzles me - why Martin doesn't have this article on his web site along side Part2 ?

Martin
When I spoke to Martin to ask his permission to use the article he asked me to let him have the scans I made from the original publication for he had lost his copy of the first part.
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  #9  
By Dave miller on 9th December 2008, 05:32 PM
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Quote:
Originally Posted by Les McLean View Post
When I spoke to Martin to ask his permission to use the article he asked me to let him have the scans I made from the original publication for he had lost his copy of the first part.
He could just post a link to this site.
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