[pure-silver] Re: fixer question - wash water xchg rate
- From: Eric Nelson <emanmb@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Tue, 3 Jun 2008 18:34:11 -0700 (PDT)
I used food coloring to test my Kostiner "archival"
washer years back and was disturbed when I saw how
long it took to run clear, so to expedite that, I dump
about 25% off the top by tilting the unit once or
twice during a 1 hour wash. Also a pre-wash after
hypo clearing lessens the carry over. I find them
very inefficient.
The only advantage to this style washer it seems is I
can leave it alone as opposed to a siphon which I need
to monitor to make sure the prints are shuffled.
So w/the Kostiner, it's 1 hour or more washing
(inefficient) but I can walk away, have dinner and
come back to deal with the prints later, or 20 minutes
of fairly regular monitoring w/a siphon.
My prints have always tested negative for any residual
fix using the "archival" washer.
Eric
--- Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
> Kodak's recommendation is that the water in the
> washing
> vessel change completely in five minutes. This is a
> bit
> misleading since a running water tank or tray
> changes
> exponentially. What is important is the rate of
> change at
> the surfaces of the paper. The emulsion washes out
> by
> diffusion, an exponential process. The rate at which
> the
> hypo leaves depends on the difference in
> concentration of
> hypo in the emulsion versus the concentration in the
> wash
> water at its surface. The greater the difference the
> faster
> the hypo diffuses into the water. Obviously, even
> when there
> is no hypo in the water, the rate will become slower
> as the
> washing progresses. If a print or film is washed in
> standing
> water the hypo will form a cloud at the surface and
> eventually reach approximate equilibrium where the
> process
> becomes very slow. The diffusion continues into the
> body of
> the water in the vessel so that the processes is
> continuous
> until it reaches true equalibrium but without
> agitation it
> will essentially stop at some point. The idea that
> hypo is
> heavier than water and will sink is a
> misunderstanding of
> the process. There may be some slight convexion at
> the
> surface but nothing more.
> The best washing is in a low volume vessel with
> continuous change of water at the surface, for
> instance, the
> spray washing found in many motion picture
> processing
> machines. Large volume tanks with relatively low
> flow rates,
> such as many "archival" washers, are less effective
> than a
> tray with a Kodak tray syphon in it, provided that a
> single
> print is washed so that both surfaces are exposed to
> the
> water. This is quite practica for RC paper, which
> also has a
> short wash time but may be a problem for fiber and
> for large
> quantity work. The best "archival" type washers,
> perhaps
> "vertical" washer is a better term, are those with
> the
> smallest volume and highest flow rate at the
> surfaces of the
> prints.
> One way of testing the flow rate of a tank or
> tray is
> to get it going and then put some vegetable dye in
> it. I've
> used the juice from canned beets. See how long it
> takes
> before the color fades to the point where it is
> visibly gone
> (again this is exponential). It should not be more
> than five
> minutes. I have a Zone VI 16x20 washer which has too
> low a
> flow rate. I use it by putting it in a bathtub and
> allowing
> it to overflow the top. I also make a practice of
> pulling
> the plug and draining it about halfway through the
> wash and
> starting over with a fresh filling. I also use a
> 16x20 tray
> (actually about 18x24) with a Kodak tray syphon.
> This will
> discharge the dye in about two minutes at a
> reasonable flow
> rate.
> One can also achieve good washing using the
> successive
> bath method. This is necessary were running water is
> not
> available or where fresh water is at a premium. Both
> Kodak
> and Ilford have instructions for this method. They
> are
> slightly different: Kodak recommends several
> successive
> baths of the same length while Ilford recommends
> baths which
> begin by being short and are successivly longer.
> This is to
> take advantage of the exponential rate of washing.
> Both are
> effective but the Ilford method probably uses less
> water.
> Since the support of fiber paper does not wash
> out by a
> strictly diffusion process it needs more time. The
> emulsion
> of fiber will wash out nearly as quickly as RC paper
> but the
> substrate (Baryta layer) and support take longer
> even when a
> wash aid is used.
> Paper and film can be tested for residual hypo
> by using
> the silver nitrate test recommended by Kodak. This
> consists
> of a solution of silver nitrate in acetic acid as a
> preservative. Its used in the same way as the
> residual
> silver test mentioned in an earlier post. A couple
> of drops
> are placed on the wet, but blotted off, emulsion
> surface and
> allowed to stand for about two minutes. There should
> be no
> more than a very slight yellow stain. The stain will
> darken
> with time so the examination should be made
> immediately.
> There is a method of fixing the stain so that a
> densitometer
> can be used to determine the quantity of hypo
> remaining.
> A true answer this question would require
> knowledge of
> the diffusion rate of the emulsion involved and also
> the
> rate of washing of the support of fiber paper. There
> are
> some actual rates mentioned in the literature but
> they are
> important only for very critical work. The Kodak
> recommendations will result in fixing and washing
> sufficient
> for good permanence.
> I try to avoid using the term "archival"
> because it is
> really very vague. True archival use implys that the
> prints
> or films will be stored in highly controlled
> conditions,
> certainly not displayed. We are mostly concerned
> with making
> our images in a way that is not overly sensitive to
> atmospheric polutants or has residual compounds
> contained in
> it which attack the image. This is not too
> difficult, one
> needs only to follow good conventional practice.
> The use of a sulfite wash aid will reduce both
> paper
> and film wash times by a factor of about six times.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
>
>
>
>
>
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