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  1. #51

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    Quote Originally Posted by Alan Johnson View Post
    I mixed an ascorbate clone of FX-1 where sodium sulfite was replaced by sodium ascorbate: Metol 0.5g ,Sodium Ascorbate 5g ,Sodium Carbonate 2.5g ,water to 1L ,pH about 11. Delta 100 was developed in this 18m 68F. It gave somewhat overdeveloped negs with a high EI.
    It is known from Crawley's experiments that if there is no sulfite the action with metol and carbonate alone is very slow.Therefore it follows that both the sulfite in FX-1 and the ascorbate in the clone must be participating in the development,but if by chemically similar reactions seems not to be known.
    BTW this clone of FX-1 is similar to a developer listed by Patrick Gainer in his article "Vitamin C developers" at Unblinkingeye.com.
    You write that the ascorbate clone of FX-1 gave a high EI. How did you measure this, by comparision to another developer? In my experience valid comparisons of EI require very tight controls in exposure and development.

    Sandy King

  2. #52
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    I would not have developed Delta 100 that long in that formula. I would have guessed at most 10 minutes. However, the point that the development with Metol-ascorbate-carbonate is very vigorous is made. The trouble with trying to compare it with Metol alone is that aerial oxidation will happen very rapidly without some antioxidant.

    Metol and sulfite in water are the only ingredients of D-23, which is quite active. If you were to develop Delta 100 in D-23 for 18 minutes you would also get overdeveloped high contrast negatives, I'll wager. Sodium ascorbate doesn't give as much pH as sodium sulfite, but if you were to add enough borax or metaborate to equalize the pH, I'll bet you will get the same activity with much less ascorbate, even though the molecular weight of ascorbate is considerably lower than that of sodium sulfite and should need more grams to get the same number of molecules.

    I have to disagree that sulfite restores hydroquinone. The data in Mees & James show that it forms the hydroquinone monosulfonate but increases induction period and reduces rate of increase of contrast. If you want to try a hydroquinone-sulfite developer without added alkali, go ahead. I think you might have to wait all day for somethiong to happen. In fact, I think I will go and do that now.
    Gadget Gainer

  3. #53

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    Sandy,
    Actually I was more interested in an approximate comparison of sulfite and ascorbate at this stage and as you say the EI measurement requires tight controls and only an approximate idea was obtained.I keep a roll of Delta 100 exposed to the same scene,average metering, sun/shade,EI 32 to 125 at 1/3 stop intervals,compare different developers using a loupe on the shadow detail against a light.I get about EI 80 for D76 1:1, the clone gave about EI 125 but was overdeveloped.
    Mainly it's interesting the sulfite and ascorbate are both superadditive with metol but it's not known if in the same way.

  4. #54
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    Again, I refer you back to Mees and James Alan.

    Chemical reactions are often slow. They can be sped up considerably by removing one of the products from the mixture. So, Metol is slow to oxidize, but add sulfite and it speeds up the oxidation. The same is true of HQ, it is slow to oxidize but it speeds up with sulfite. This is NOT superadditivity, but merely shifting the balance of a chemical equation. (if you substitute the word 'develop' in the above for the word 'oxidize' then you have the nature of the reaction in a developer).

    In Mees and James they offer proof by using a different oxidant and demonstrating the same effect in the presence and absence of sulfite as we see in a developer. They show that this reaction is general, not just specific to a developer solution.

    Mixing Metol and HQ together gives a synergistic reaction (superadditivity) that is different than the effect of sulfite. Sulfite speeds up this reaction as well, but by changing the reaction constant.

    A + B * K = C where K is a constant. A and B are an oxidant and reductant respectively and C is the oxidized B (oxidized reductant).

    A + B + D * K * KK = C + D = E where K is the original constant and KK is the constant supplied by removing C from the right of the equation by the action of D. Therefore, in the second reaction D = sulfite and C = Quinone and E = HQ monosulfonate.

    This equation is a simple, non-balanced version of the redox reaction of HQ in the presence of silver halide and with and without sulfite. It is not even written in classic chemical terms. In those terms the "=" is changed to an arrow "->" or a double arrow (one in reverse "<-") with "K" above the arrow and "KK" or K1" below the reverse arrow plus other modifications. These cannot easily be shown without graphics.

    PE

  5. #55

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    PE,
    I wonder if you would care to comment on speeding up the reaction by ascorbate. Did Mees & James know about this? By the explanation you quote metol and ascorbate would not be considered superadditive. Is that the picture?

  6. #56
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    I didn't say that.

    Mees and James don't comment on Metol + Ascorbate superadditivity AFAIK, nor has Haist, but my memory may be faulty. There was so much done with HQ + Metol that that is what I remember. I do know that we used an EAA (Elon (Metol) Ascorbic Acid) developer for research purposes, and I believe that the formula is in Mees and James, if not Haist.

    PE

  7. #57
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    Let's refer back to the graph I took from Mees & James that shows the effect on development by Metol of hydroquinone OR sulfite OR ascorbic acid at pH=8.7. The effect of hydroquinone is nil. The line is flat at each development time. The effect of sulfite at each development time increases with amount of sulfite, levelling off at about 0.05 moles/liter. The effect of ascorbic acid is the same.

    What was missing from this graph that cannot be deduced from it is the effect of both hydroquinone and sulfite on development by Metol at pH = 8.7. I do not see that treated anywhere in the volume.
    Gadget Gainer

  8. #58
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    Superadditivity is addressed in CH 13 of Mees and James (P299ff) and Chapter 16. The discussion is touched off by using Phenidone as an example.

    PE

  9. #59
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    Quote Originally Posted by Photo Engineer View Post
    Superadditivity is addressed in CH 13 of Mees and James (P299ff) and Chapter 16. The discussion is touched off by using Phenidone as an example.

    PE
    That discussion does not mention the presence of sulfite. How much of the activity is due to phenidone and sulfite?
    Gadget Gainer

  10. #60
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    Sulfite is not superadditive, it merely changes the kinetic equillibrium as I have described previously.

    It can only do so, according to Mees and James, if it reacts with a product of the development reaction produced by one of the developers.

    PE

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