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Thread: PyroCat HD

  1. #31
    Ole
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    Thank you very much, mr. King!

    I'll try this with the next batch of film, at the moment the weather's so bad I wouldn't go outside myself, much less with a camera!

    My gripe with the percentage is this:

    Adding 1g chemical to 100cc water is a 1% solution, or at least very close to it.
    Adding 100g chemical to 100cc water is a 50% solution by weight (100+100=200), NOT 100%.
    Taking 100g chemical and adding water to 100cc, the concentration depends on the density of the chemical, but as it will contain 1g chemical per cc of solution, I might be willing to let it pass as 100% - although it's wrong...
    -- Ole Tjugen, Luddite Elitist
    Norway

  2. #32

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    I am frankly quite confused by the question of percent solution. Out of curiosity I just added 100g of potasssium carbonate to 100ml of water. This gave a total volume of 137ml of Pyrocat-HD stock solution? Would I be correct to assume that this constitutes a percent solution of potassium carbonate of approximately 73%, i.e. 100/137?

    Regardless of any confusion about how to determine a percent solution the formula at Unblinking Eye is correct: 100g of potassium carbonate in 100ml ofwater.

    Sandy King


  3. #33

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (sanking @ Apr 2 2003, 05:15 AM)</td></tr><tr><td id='QUOTE'>I am frankly quite confused by the question of percent solution. Out of curiosity I just added 100g&nbsp; of potasssium carbonate to 100ml of water. This gave a total volume of 137ml of Pyrocat-HD stock solution? Would I be correct to assume that this constitutes a percent solution of potassium carbonate of approximately 73%, i.e. 100/137?

    Regardless of any confusion about how to determine a percent solution the formula at Unblinking Eye is correct: 100g of potassium carbonate in 100ml ofwater.

    Sandy King</td></tr></table><span class='postcolor'>
    You are making things much too complicated. You want to add a given weight to a given volume, so it makes it easy to add a desired amount per volume.
    For instance::

    Add 50 grams sodium carbonate to 50 ml of water, dissolve, and add enough water to &#39;make&#39; 100 ml of solution. You know that to get 1 gram of carbonate into your final batch, you need to add 2ml of your solution, it&#39;s a 2:1 ratio.

    Forget about percents...

    If you would like, point me to a process you are trying to work out, and I will show you how to streamline it.

    I am sorry if I sound a little bossy, I may be a baby at photography, but I do know chemistry.

    --Aaron
    art is about managing compromise

  4. #34
    Ole
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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (sanking @ Apr 2 2003, 05:15 AM)</td></tr><tr><td id='QUOTE'> I am frankly quite confused by the question of percent solution. Out of curiosity I just added 100g of potasssium carbonate to 100ml of water. This gave a total volume of 137ml of Pyrocat-HD stock solution? Would I be correct to assume that this constitutes a percent solution of potassium carbonate of approximately 73%, i.e. 100/137?
    </td></tr></table><span class='postcolor'>
    All that means is that the finished solution has a density of 1.46 SG - so 1ml weighs 1.46 gram. Your 200 gram total has a volume of 137ml, 200/137=1.46. So the concentration of the solution is 73% weight/volume (correct&#33, or 50% weight/weight...

    With "normal" solutions up to about 10% or so this differende can be neglected, but with this kind of concentration it can be very confusing - and imprecise.

    A better way to make the specified solution B would be to take 73g potassium carbonate and add water to 100ml. This gives a specified amount of chemical in a specified end volume - so I know what size bottle to put it in...

    -- Ole Tjugen, Luddite Elitist
    Norway

  5. #35
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  6. #36

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    There is nothing really wrong with making solutions this way, it is just confusing, and is inconsistent from the way the other solutions are mixed.

    What i really hate is when differnt units are used, like the ABC formula on Ron Wisner&#39;s site. Mixing grams and ounces gives me a headache.
    art is about managing compromise

  7. #37

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    Ole, I use it just as Clay specified in his article, for pt/pd printing I use 1:2.100. But I suppose for normal silver printing the 1:1:100 solution would work just fine.

    As to the percent solution Ole is correct if one wants to be absolutely accurate. With low percent solutions the change in density is minimal and thus it can be ignored, at high concentrations, such as a 50/50 it is important, but for photographic purposes the "nomenclature" can be ignored and use the mixing instructions as given by Sandy. One more wrinkle would be that a true 100% solution would probably not dissolve as it has reached its saturation point. This is why 100gr of NaCO3 can dissolve in 100 ml of water, as it has not reached its saturation point, since it is only a 73% solution as explained above. In any case dont worry about it, just do it as Sandy said, it works great.

  8. #38
    Ole
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    Oh, I&#39;ll try it - as soon as I have some new negatives to develop. Tomorrow, or thereabout

    The main reason (besides being really uptight when it comes to chemistry) behind my inquiry was that I have no potaiium carbonate, so will have to substitute something else. Or wait a month, which I don&#39;t want to do. So I wanted to know what to make of the recipe as stated (a formula requires a bit more precision, IMO)...

    So I&#39;ll work out the equimolar sodium equivalent of the 73% weight/volume potassium carbonate solution, and happily try that&#33; I&#39;ll even post the results here.


    BTW; it&#39;s possible to make more than 100% solutions of some chemicals. Hypo springs to mind - the crystalline version contains more water than a saturated soltion would...
    -- Ole Tjugen, Luddite Elitist
    Norway

  9. #39
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    I can&#39;t say that I&#39;ve actually tried this, but I have heard that the pH+ often found in pool supply stores is reasonably pure potassium carbonate. You might want to check around and save yourself a wait.

    Clay [saturated at an 11% solution :^) ]
    I just want to feel nostalgic like I used to.


    http://www.clayharmon.net - turnip extraordinaire

  10. #40

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    It is my understanding from readings in Mees and Haist that in most developing formulas potassium and sodium carbonate are interchangeable on a per weight basis, though I have never considered the difference in molecular weight. Just making allowance for monohydrate and anhydrous forms gives me enough of a headache as it is without looking for more trouble.

    In any event, all of my experiments (which include extensive testing with curve plotting) show that in the pyrocat formula the sodium and potassium forms of carbonate can be substituted on a one to one ratio in terms of weight, with no change in the working characteristics of the developer. In fact, all of my earlier experiments with Pyrocat were carried out with sodium carbonate with B solutions of 10g - 20 g of carbonate to 100ml of water. Later I found that potassium carbonate would go into solution at a much higher concentration that sodium carbonate and decided to switch to the 100g potassium carbonate to 100ml of water because it allowed a very practical dilution of 1:1:100.

    So the bottom line is that you don&#39;t really need to test this premise. I call tell you for a fact that a 1:5:100 working dilution mixed from a B solution of 20g sodium carbonate per 100ml of water will give curves that are virtually identical for the same time and temperature of development as a 1:1:100 working dilution mixed from a B solution of 100g of potassium carbonate per 100ml of water. The fact that the 1:5:100 solution is slightly more diluted than the 1:1:100 solution does not appear to result in any measurable difference in the curves.

    And I guess that is just about all of the meaningful information I can share with you on this subject&#33;&#33;

    Sandy King

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