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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
Default Page 4


Water exchange relative to tank volume

In the real world, total dump and replacement washes become impractical where large numbers of prints are concerned. Although it’s possible to dump quickly, the refill time makes the method impractical unless supercharged plumbing arrangements are made. The Salthill archival washer appears to be the exception to the rule – David Katchel’s review of the unit states that its rapid dump/fill feature is unique among archival washers. I have yet to see or use one, as they are not distributed in the UK.

A 16 x 20 13-slot Nova tank has a volume of about 50 litres; with a typical throughput of a 4-5 litres/minute there is a refill time of 10 - 12.5 minutes, and the print will be uncovered for most of this time. (Additionally, washing action might be different at the bottom and the top of the print.) Sinks, as opposed to slotted washers, do exist to perform this type of wash efficiently. In the UK, the Epic brand has a 100 litre wash sink that dumps, using a siphon of the type utilised in men’s’ toilets. Water filling can be extremely rapid. The only problem is that the high forces involved in filling and dumping are stressful to large prints. The kinked and corrugated prints I’ve seen emerge from such washers would never be described as “fine”.

A washing tank has a relatively high volume compared to the volume of prints being washed in it – for example, a 16 x 20 washer may contain 50 litres of water. Washing a volume of about 750 ml paper when fully loaded. An average water throughput is about 5 litres per minute, which will result in a volume equivalent to about 12 exchanges during a two hour period. This does not mean that in 10 minutes from the start of washing the washer contains fresh water, or even 30 minutes later. Diffused thiosulphate is only gradually being transferred out of the tank, and a certain amount remains right to the end of the wash. To offset any effects on diffusion, and to improve agitation, the economical solution is to reduce the tank volume.

When using spray washing this is taken to the extreme. I tested this when investigating washing emulsions applied to ceramic surfaces. The water from a shower head was passed over the ceramic surface for 10 seconds per minutes, draining into a sink. Consequently the water volume present at the surface of the vertically washed piece approached zero. Efficiency was compared to a control specimen continually washed in a dish using a Kodak tray siphon. There was no practical difference between the qualities of washing of the two methods, from which we can infer that as long as a film of fresh water is present at the surface of the material for salts to diffuse into, washing will proceed effectively. Regular replacement of the water film by passing the shower head across it ensured this. Although not tested, it seems a reasonable inference that continual spray washing will be more effective than tank washing; this is confirmed by Neblette, and it is a washing technique used in some rapid access film processing systems.

From dye injection tests, it is evident that a higher volume of water in the compartment serves to act as a reservoir, slowing down water exchange. An individual cell or compartment in an archival washer can be effectively doubled in size to check this effect by removing one divider and blocking one inlet jet. The dye persists longer, illustrating that the hypo level in the water persists at a higher concentration. The traditional view is that the washing rate is retarded by thiosulphate build-up, and while tests such as David Vestal’s washer review show a slower wash rate in larger volume tanks, could the dominant effect be due to inferior agitation? All I can conclude for sure is that, for a given water flow, larger cell volume does not help. Extrapolating this principal means that a cell containing virtually no water is the most efficient, with the ideal being complete total water exchange at regular intervals, or possibly washing with continual laminar flow. Reducing the internal cell capacity to a safe minimum is the nearest way of approaching this in a constant flow washer. SaltHill follows this principle; the cell width of their washers is 1 cm. Nova opted for a cell width of 1.5cm on their 13 slot washers and this seems to be a good optimum. The print is not too difficult to insert, and there is sufficient capacity to induce an efficient sweeping water action.



Further controls in washing

Pre-Rinsing:


Introducing a print straight from the fixer directly into the washer is not helpful. You begin the wash having dumped a load of fixer into the compartment that wasn’t even in the paper structure to start with. If you can pre-rinse even briefly prior to washing, you avoid filling the cell with concentrated fixer, thus cutting the steepest part off the washing curve and easily ten minutes off your time. You can adopt part of the special Ilford sequence and employ a five minute pre-rinse, followed by hypo clearing and the main wash. A water saving pre-rinse bath is easily set up when using most archival washers simply by using the overflow from the washer.


Hypo Clearing:

The importance of hypo-clearing agent as a wash aid cannot be over-stressed. It is inexpensive, environmentally harmless, and its use results in lower levels of residual thiosulphate than can be achieved by washing alone, as well as a considerable saving in water. In addition to the thiosulphate displacement, wash aids help reverse the mordanting of thiosulphate in the image silver that takes place when aluminium hardeners are used, and help remove the sparingly soluble silver thiosulphate complexes that cannot be removed by washing alone. A further attribute is that cold-water washing is more effective after the use of hypo clear. Both the Kodak product and Ilford Galerie Washaid are similar. The Ilford product is slightly more alkaline, which should improve its efficiency marginally, and it contains agents to balance it for hard water. A number of other brands exist, including Heico Perma Wash. For scratch mixers, a 2% solution of sodium sulphite (about a heaped teaspoon in a litre of water – measurement accuracy is not critical) works well.


Hypo Eliminator
:

Hypo eliminator is frequently confused with hypo clearing agents. It is a completely different substance, performing a different function. Hypo eliminator is a mixture of ammonia and hydrogen peroxide, prepared immediately before use. Whereas hypo clear acts by displacement, hypo eliminator actually breaks thiosulphate down by oxidising it into soluble sulphates that are more readily removed. Until the 1980’s, the use of hypo eliminator was recommended for the ultimate in archival work, and was included as a benchmark in the ANSI standard. Current thinking is that the cure is worse than the disease, as it weakens the paper structure and may have long term effects on image stability. Hypo eliminator is no longer recommended.

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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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