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  1. #21

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    Quote Originally Posted by gainer
    Actually, the expression originally referred to Newcastle in the British Isles. I was referring to your lecturing Sandy King about pH.
    To be precise.

    Carrying coals to Newcastle.

    1. To do something that is obviously superfluous;
    2. Used to describe a foolhardy or pointless action.
    3. To describe or add to something for which an excess already exists.

    Logic of the expression. Newcastle was historically an area where coal was mined in great abundance. It woul therefore have been a ridiculous and pointles action to carry coals to that place.

    Rough equivalents in other languages.

    French Porter de l'eau à la rivière Water to the river
    Portuguese Vender mel ao colmeiro Sell honey to a beekeeper
    Spanish Echar agua al mar Throw water into the sea

  2. #22
    fhovie's Avatar
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    Now I am confused - It seems in a previous post - Sandy quoted Hutchings as stating that ascorbic acid as well as phenidone would create very low accutance/adjacent effects. Now here Patrick has quoted Suzuki stating that accutance is greater with ascorbic acid. I notice that accutance is pretty good with XTOL and not very good with PC TEA. I had thought that it was the sulfite in the mixture that helped create the accutance. TEA may be a good buffer and stableizer but not a silver solvent needed to cause silver grains to erode and redeposit on the edges - as I have read from Anchell. What is the truth of this? anyone?
    My photos are always without all that distracting color ...

  3. #23

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    Quote Originally Posted by jdef
    .... Hypercat is not well buffered, works at high pH,....

    Jay
    So maybe Hypercat and Pyrocat-HD are opposite in their behaviour when diluted for stand/minimal agitation development. The hydroxide is so poorly* buffered that increasing the ratio of B/A might be needed to keep the developer going, but in the case of Pyrocat-HD, the carbonate is much better buffered, and doesn't need the ratio of B/A increased.

    This is merely armchair conjecture. I have used Pyrocat-HD a lot at 100+0.6+0.6 with minimal agitation for about 18 minutes and it still has plenty of power left to increase contrast if development is extended. (I use 500mL for one 120 roll)

    * by using the word "poorly" I am not being derogatory. I understand the benefit of local developer exhaustion (edge effects).

  4. #24

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    Quote Originally Posted by sanking
    My experience is that the opposite is true, i.e. for stand dilution with long development times it is better to slightly incrase the proportion of A to B. Having more A in the working solution seems to slow down the rate of exhaustion and results in less general stain. If one increases the prorportion of B to A, the result (at least my result) is more general stain, even with slightly shorter times of develoment.
    Sandy - I did expect this to be part of the observations with this approach - a higher base+fog or stain level.

    But I now see that I failed to mention a very important part of my question in the original post - what happens to the edge effects. (Sorry about that... I didn't mean to send people off on a wild goose chase.)

    I take it this is why Patrick was talking about glasses of water and other such metaphorical euphamisms. I suspect he thought I was only concerned with the over all H&D curve of the prcessed film. I was really interested in using this technique to get increased adjacency or edge effects - the microdensity effects.

    So yes, higher stain/fog would be expected due to the developer being more active, but do the adjacency effects benefit from this approach?

    I can see that one may reject the results from initial tests of these dilutions because of the higher stain, but if adjacency effects benefit, then the increase in fog/stain may be worth it.

    Kirk - www.keyesphoto.com

  5. #25

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    Quote Originally Posted by Photo Engineer
    Kirk, I'm rather amused at this thread.

    I can understand criticism of using a microdensitometer as being to expensive and 'technical' for common usage in the other thread, but here you are dragging pH into it.

    Now, even with pH meters being so inexpensive, how many times do we see people discussing the pH of their developer, or adjusting the pH in their experiments to insure batch to batch uniformity? Seldom, right?

    I think that your direction has merit, but as for quantifying it or getting repeatable results it will not happen until the pH and buffer capacity are documented for all of the conditions. This will probably draw a lot of criticism, I'm sure, but some of the effects of stand and dilute developers are due to halide edge effects, and others are due to pH effects (buffer exhaustion) and no one has gone to the trouble of distinguishing between them, even though they do different things and act different ways.

    In the other thread, you propose standards, but standards imply measurment and numeric values and this was negatively viewed for the most part.

    I think your suggestions here and earlier have great merit. Keep it up. Non illegitemati carborundum (just in case they try).

    PE
    Ron - glad to brigthen your day!

    Yeah - I wish there was a reasonable inexpensive approach to the microdensity issue - I would certainly spend several hundred dollars (probably more over time!) to get a system that could give me this type of info. Simply because it would allow my film/developer testing to go to the next level of information.

    And that is a good point about using a pH meter to check formulation consisitency. I have never done it other than on a very occasional basis. I have titrated a few things - such as when I was attempting to reverse engineer Xtol back when it came out.

    But yes - excellent point on the buffering capacity being just as important as pH. My proposed approach would certainly greatly increase the buffering capacity (alkalinity) of a developer. And as Sandy pointed out, diluting Pyrocat doesn't change the pH significantly with dilutions from 1+1+100 to 1+1+400. But the bufering capacity is going to be 1/4th as much in the second dilution. And in the dilutions I suggested it would be 4 or more times greater.

    Side note: I'm always amused when people say that their tap water has a pH of such and such, and that's why it is unsuitable for some particular application. Without knowing the buffering capacity, i.e. the alkalinity or less frequently the acidity of that water, they really can't make any such claims. There's a whole lot more to water chemistry than just pH.

  6. #26

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    Quote Originally Posted by Tom Hoskinson
    Then again, I don't mention my microdensitometer either...
    Tom - are you joking about having a microdensitometer, or do you really have one? Could you describe it some and how you use it?

  7. #27

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    Quote Originally Posted by Photo Engineer
    As buffer capacity decreases, the production of hydrogen ion becomes gradually more and more significant in the overall reaction, and begins to have its own effect similar to bromide in edge effects. It does not 'drag' in the classical sense of 'bromide drag' due to the lighter nature of hydrogen ion, but rather it tends to diffuse further in all directions.
    So maybe the hydroxide approach like Jay is using would be "better" for getting more edge effects due to the poorly buffered nature of hydroxide solutions? That also could explain why the Rodinal people seem to like it for this type of development?

  8. #28

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    Quote Originally Posted by sanking
    OK, but what is the relevance of this, for this discussion, to a developer that when mixed has a given pH, and at the end of devleoment has the same pH.

    Based on one of your previous messages I assume that it has something to do with the pH in border areas of heavy and light densitities where the developer is exhausting more than in the general solution. But if so, specifically how does this relate to a developer that begins with a general solution of around pH 10.9 and maintains that pH throughout the development.
    The relevance is that for two developers with the same pH, the one that is least well buffered may show different effects than the one that is better buffered when looking at the behavior of the developing agents at a microscopic level in the developer.

    Especially when one starts to consider that these reactions are going on inside a gelatin matrix that is affecting the diffusion rate of reagents in and out of it, and then we go and do things like not agitate the solution that is in contact with the gelatin matrix to even further minimize the replenishment of fresh reagents into the gelatin.

    Inside that gelatin, the pH of the developer soution will drop as the silver metal is reduced from the silver halide. So this is where the buffering capacity of the developer will come into play.

    When the carbonate (or cabonate buffer) is present, the pH will change less when the supply of fresh reagents is limited because of the buffering capacity than when a hydroxide solution is present, which has little buffering.

    Part of what makes carbonates (and phosphates) much better buffers when compared to hydroxides is that they have more than one negative charge on them. Carbonates have 2 negative charges, phosphates can have 3.

    When you add acid to a hydroxide, you start to neutralize it. One acid (H+) added to one hydroxide (OH-) and then you get water, H2O. Ron mentioned that mixed salts do a much better job of buffering and have a higher buffering capacity is because they have the capacity of react with the added acid but not change the overall composition of the solution significantly.

    If you have a solution of CO3-- (carbonate) with some HCO3- (bicabonate), and you add acid, you convert some of the cabonate into bicarbonate (H+ added to CO3-- gives you HCO3-). If you have sufficient excess of carbonate or bicarbonate in the solution, the ratio of the carbonate to bicarbonate does not change significantly with the addition of that acid. That's why a carbonate or bicarbonate solution is better buffered than a hydroxide solution.

    The same goes for a pure carbonate solution. You add acid to it, and I think you can see it does not neutralize the carbonate. It forms bicarbonate. And then this starts to form a mixed salt and buffered solution.

    The thing to watch out for is when you get the amounts of carbonate and bicarbonate in equal amounts. (I mean Normal concentrations here in the chemistry sense of the word "Normal", i.e. "equivalent" amounts, not "equal" molar or gram or percent amounts). When this happens, the solution does not have any buffering capacity, and the pH will drop quickly as acid is added to the solution. The solution is at an "equivalance point" where there are equal normal amounts of each buffering ion and the buffering capacity is lost.

    Here's a link to a nice little method for determining alkalinity - that can show the buffering capacity of a solution. http://water.usgs.gov/admin/memo/QW/qw82.05.html

    And another link that does a good job discussing alkalinity and buffering - http://www.advancedaquarist.com/issu.../chemistry.htm (note there is a typo in Eq. 1, the CO3 should be CO3--.) THis page also shows a titration graph of a carbonate solution that demonstrates how the buffering helps maintain pH as acid is added. Make sure you scroll down to wher he has the graphs for where he added sodium acetate to the water and see how well that addition buffered the water, and note the pH range the acetate was effective at.

    And finally, some good titration curve examples that show the pH change at the equivalence point: http://www.chemguide.co.uk/physical/.../phcurves.html

    (Sorry about the more indepth than usual chemistry discussion for those that are not into this sort of thing.)

  9. #29

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    Quote Originally Posted by fhovie
    TEA may be a good buffer
    TEA is not considered to be a good pH buffer. At least not solutions that are TEA based only.

  10. #30
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    Quote Originally Posted by Kirk Keyes
    So maybe the hydroxide approach like Jay is using would be "better" for getting more edge effects due to the poorly buffered nature of hydroxide solutions? That also could explain why the Rodinal people seem to like it for this type of development?
    Where is it written that more edge effect is better? Everything I have read about it is that some is good, but a point is reached where enough is enough and more is too much.

    If you get too much in your negative, what can you do to undo it? Are we looking for a photograph that will be judged by the clarity and width of its Mackie lines? "Ooh, what nice Mackie lines" the judge said, without commenting on the subject matter and gradations.

    Hydroxide or no, Rodinal is capable of infectuous development. Fine white lines become wider in photographs developed in Rodinal. This means that silver has spread from its appointed place in the negative during development.
    Gadget Gainer

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