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Thread: Highly Dilute KRST Capacity - Published Specs?

  1. #1

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    Mar 2005
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    Highly Dilute KRST Capacity - Published Specs?

    While I've been selenium toning some (not all) of my work for years - I've typically used a 1:19 dilution, with a goal of just a slight shift in Dmax and tonality.

    ...and while the published data regarding solution capacities all seem to apply to a 1:3 dilution - I cannot find any reference to capacities while using much higher (such as my 1:19) dilution - so I've basically just been throwing this away when toning times get excessive. Pretty much standard operating procedure with others on this forum as far as I can tell.

    But...are there any published references to KRST capacities at high(ish) dilutions? Or does this simply relate in a linear fashion like it does for film...as in square inches per total amount of concentrate present in solution?

    The reason I ask is that my technique of just lengthening times to compensate for variable solution activity can give me results that are visibly inconsistent (which bugs me) - and I'm wondering if either I'm doing something wrong or if there might actually be some other changes in the aging KRST (other by-products, etc.) which might give such inconsistencies...and if so, then I'd truly like to know more about what others feel about reasonable capacities for higher dilutions.

    ...understanding that I could just throw out a given batch of KRST after each session - but this seems wasteful, expensive, and environmentally unsound.

  2. #2

    Join Date
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    Re: Highly Dilute KRST Capacity - Published Specs?

    John,

    My standard operating procedure is much different than you describe. Maybe you've missed my numerous posts on replenishing and reusing selenium toner. Here's a quick description:

    When toning times get too long, add a bit of concentrate to the working solution. In your case, it would not be much, since you're working at a relatively weak dilution. Add bits at a time till toning times come back into an acceptable range.

    With replenished toner, a precipitate often forms (silver selenide I believe). This needs to be filtered out. I filter my toner before and after use, i.e., when pouring into and out of the storage bottle. Good-quality coffee filters have worked fine for me for years. Even toner with particles suspended in it has no adverse effects on the print.

    That's it. Your toner will last for years this way (I have some much older than 10 years and it's still going strong). Another advantage is that the ammonia odor disappears almost completely from the toner; toning activity remains just the same. I test every batch of prints for residual silver and hypo. All are just fine. Many printers I know have adopted this regime and use it to good effect.

    As for "visual inconsistencies": I tone visually, deciding by eye when the proper amount of toning for a specific print has been reached. All I can say is that weaker toner for a longer time seems to match stronger toner for a shorter time rather well. However, my method allows you to keep the toning times in a rather small range of time (I like 4-6 minutes). So, you really shouldn't have to tone for a long time in weak toner to get the same results as, say, 4 minutes in stronger toner. Just keep the toner strength fairly consistent by adding a bit of concentrate when times reach the limits of your comfortable range.

    As for "published capacities": After the first print toned in fresh toner, you will need a somewhat longer time for the next print to reach exactly the same amount of toning. Simply running 40 prints through toner and 1+x dilution and expecting them all to be the same is obviously unrealistic, since the toner begins to lose activity with its first use. As mentioned, I tone by eye (under good lighting designed to replicate what I think is ideal gallery lighting) and keep both an untoned print and the first "keeper" toned print nearby for comparison. For 4 or 5 of the same print, the time will remain, for all intents and purposes, the same, but the times for prints on the same paper at the end of the session may increase 40% or more. Another advantage to toning by eye is that you are finding the most pleasing amount of toning for every particular image. Different prints need different amounts of toning to look "right" because the distribution of densities and important areas is different from print to print. Keep in mind that Kodak's published capacities date from an earlier time when discarding photochemistry was easier and environmental concerns were pretty much non-existent. Their method was simply to toss the toner when toning times got too long for comfort. That sells more toner for them too... Replenishing ensures that you'll always have active toner and never have to worry about "capacity."

    Did I mention that this is much more environmentally friendly and economical as well?

    Hope this helps,

    Doremus

  3. #3

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    Re: Highly Dilute KRST Capacity - Published Specs?

    In practice, it is different from the specs or other photo solutions...

    Metallic toning depends on a concentration of metallic compounds in solution... When the bath is fresh, there is more metal in it, and as it gets used, there is less until it is depleted... The metals are attracted differently to a high or low key print image densities, so that's a big variable... Also the first print in the bath gets the most activity, where much of the excess of the metal is attracted to the print, and less is available for the following prints... The solution they are in are just a medium for the metals to remain suspended it, but also supply the pH, and environment for the image to be toned... So metals concentration will change during the toning process, thus changing solution working life...

    You can look in old photo books about the working process of when gold toning was used extensively (before the turn of the last century) where it is mentioned that for the first print, most of the gold goes to it, so 3 prints would be in the first run where it would distribute the gold more evenly, and single prints would go in later, and after a few prints, the bath was exhausted and need replenishment...

    You would have to develop your own working solutions usage table, but it would also depend on size, volume, and if a hi or low key print run...

    Steve K

  4. #4

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    Dec 2014
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    Suwanee, GA
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    Re: Highly Dilute KRST Capacity - Published Specs?

    Make a few test strips using a step wedge or your own intervals with black to near white tones. When solution is fresh drop one in and note how long it takes to affect color at each tone (darkest first color shift at edges 4mins, midtone 7mins, highlights 10mins).
    Then after a few prints repeat and compare your times. I find the Dark tone time is nearly the same but the highlights take longer.

    If your goal is not to affect color you will have the max time you can leave in based on the dark time, But do the full test every time. You may also notice that the color tone is different from the early tests to later tests.
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