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Why Pyrol rather than hydroquinone?

NER - did you know that XTOL generates a stain? It does, bleach some XTOL processed film and you will see a very faint magenta stain. It's not enough to have a significant effect, but it is visible.
 
Kirk, he's going to ask you where you read that, so hit the books!
 

Thank you very much for the citation and quote.
 
NER said:
Why is asking for verification of a statement so unusual and a cause for ridicule?
Click to expand...

He just told you what he has observed. To ask him to "verify" the evidence of his senses by citing a peer-reviewed work seems more than a little superfluous.
 
NER - I think he was referring to the general tone of the preceding discussion. Don't worry about it.
 
I find this argumentation quite amusing. In my years of experience as a research engineer, I have seen several instances where theory was cited as a reason for some experiment not working, whereas in fact it did work.

One thing you must remember. In years gone past, the image stain left by development was a nuisance to be avoided. You could get that impression from the works of Hurter and Driffield. It happens that the stain left by hydroquinone is mostly avoided by having anything like the usual amount of sulfite in a working solution. Furthermore, in order to get the optimum superadditivity between hydroquinone and either metol or phenidone, a certain amount of suldite is required. That is almost as much as it takes to prevent staining. The ordinary experimenter would not see any staining by hydroquinone, because who compounds an MQ or PQ developer without at least 10 grams of sodium sulfite per liter? I found it for myself because I was interested in sulfite-free developers. Not for environmental reasons, but because sulfite free developers tend to be surface developers that are not hindered as much by the surface charge barrier (I hope I got it right, but really don't care.) You can find such statements in "The Theory of The Photographic Process".

So, I thought I found that hydroquinone in alkaline solution does make a staining developer. Then I found by reading a book that I was right, by gum! I'm glad I found that book. Otherwise I might be hiding in a corner in denial somewhere, fearing I had seen an imaginary ghost image.
 

I thought I remembered such a comment, too, so I went and skimmed the rest of the article, and it's on p. 25: almost exactly the phrase you use, in parentheses, followed by "Hydroquinone is 1,4-dihydroxybenzene. Pyrocatechol is 1,2-dihydroxybenzene. According to theory(1), any developer with two or more active hydroxyl groups will be an active tanning and staining developer." The footnote ("(1)" above) then offers chapter 13 of W. H. Lee's _The Theory of the Photographic Process_ as a citation. I don't happen to have that book to cite it directly, though.
 

I can only wonder what is going on with that hydroquinone.
That 2 grams/liter is also a Lith developer sulfite maximum.
Reconcile, if you will, HQ's oxidation products giving lith
development and at the same time those oxidation
products being involved in tanning gelatin. Dan
 
The lith developer may very well be tanning and staining - or it may be that the design of the lith film emulsion prevents/suppresses it. In any case, Bleaching the silver out after development and fixing seems like a good way to tell.
 
I don't recall seeing any formulas for MQ or PQ lith developers. Hydroquinone substituted for catechol in Pyrocat HD will produce a stain image. It is different in color, as the previously posted information says. Sandy King does not find the color as effective for his purposes as catechol.

Hydroquinone, catechol or pyro in TEA can make a single solution staining developer stock solution. The pH won't be high enough to make a lith developer. I think maybe the high silver contrast of lithography keeps whatever stain image there might be from showing.
 
There is nothing in Xtol to cause a stain image to form. The oxidation products of isoascorbic acid are colorless and more importantly water soluble. If you are seeing a slight magenta stain then this is a small amount of antihalation dye that has not been washed from the film. The oxidation products of Dimezone-S (the other developing agent in Xtol) are also water soluble.
 
I should have mentioned that some lith developers depend on the reaction between sulfite and formaldehyde to produce NaOH in the working solution. These are two part developers. The sulfite preserves the hydroquinone in one bath. The formaldehyde is added at time of use. The amount of excess sulfite is probably enough to prevent staining.
 

Gerald - this may be so, but I've taken an XTOL-processed neg (I think it was FP4+ or Tri-X) and bleached it and there remains a magenta image. Very, very low contrast, and as I said probably too low to make any contribution to the print.

If it is residual antihalation backing - that may be, but after all, it appears identical to a "stain".
 
Tom Hoskinson said:
The lith developer may very well be tanning and staining - or it may be that the design of the lith film emulsion prevents/suppresses it. In any case, Bleaching the silver out after development and fixing seems like a good way to tell.
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Perhaps the high density of the lith image makes the stain not noticable.
 
Kirk wrote: "Gerald - this may be so, but I've taken an XTOL-processed neg (I think it was FP4+ or Tri-X) and bleached it and there remains a magenta image. Very, very low contrast, and as I said probably too low to make any contribution to the print.

If it is residual antihalation backing - that may be, but after all, it appears identical to a "stain"."

From the 'Thoughts off the top of my head' department:
Ascorbic acid is a very weak tanning agent, which appears to be helped by the presence of borates. Could it be that the very slight tanning effect makes any dye slightly more difficult to wash out? I realise that there are theoretical reasons to discount this explanation.

Best,
Helen

PS Dan, if you call tanning and staining 'the same' then we apply different meanings to the word same, that's all!
 
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I don't think it would be antihalation dye which was left after developing - sensitizing dye is far more likely (unless we're talking 35mm, where the antihalation dye isn't on the back side of the film).

It is conceivable that some of the dye might get preferentially left in the "hardest" part of the emulsion, i.e. where the silver density was highest and tanning strongest.
 
Helen, Ole, you guys make good points about the "hardening" of the processed areas with greater optical density possibly making it harder to wash out the dye, whether the dye is antihalation, sensitizing, or other. Not a true tanning or staining process, but one that results in a "stain" nonetheless.

I haven't checked with other non-staining developer/film combinations so I can't say this behavior is unique to the XTOL. Perhaps someone else here has?
 

I have also observed a slight amount of staining with PC-TEA, which is ascorbic acid + phenidone in TEA. It amount to only about log 0.05-0.10 and would not be apparent unless one were to compare densitoimeter readings in Visual and Blue channel.

Sandy
 
 
 
gainer said:
When are those things not in intimate contact?
What sulfite levels are we talking about?
Click to expand...

Specifically the chemical products of reduction, in so far as
tanning and lithing, are not present when sulfite levels are high.
That or some other explanation for their being present and
a lack of tanning or lithing.

I think it must be the quinone which causes the tanning. Lith
results are dependent upon it's presence. Is it possible for both
tanning and lithing to proceed simultaneously? The conditions
for both to proceed concurrently are present.

Maximum sulfite levels for tan and lith results are both
the same, 2 grams per liter. Dan

BUT TEA MAY. By that I mean the ph of a TEA solution
containing hydroquinone and a pinch of sulfite may be high
enough to initiate silver halide reduction. Dan
 
I'll check again, but I'm pretty sure you can get a stained silver image with just hydroquinone and TEA in water. No sulfite required. If you want superadditivity with phenidone or metol, a modicum of sulfite is required. I'm also pretty sure that you won't get high enough contrast to call it a lith developer. If you then add some paraformaldehyde, the pH will go way up because of its reaction with sulfite. A lot of fog will result unless you add two or three bunches of bromide. I'm speculating somewhat, but the formula I got for "extreme contrast films" from the 1941 War Department Technical Manualon Basic Photography is:
water at 125 F.....................................................64 ounces
sodium sulfite (des.)..............................................4 ounces
Trioxymethylene (paraformaldehyde).........................1 ounce
Potassium metabisulfite..........................................150 grains
Boric acid crystals.................................................1 ounce
Hydroquinone........................................................3 ounces
Potassium bromide.................................................90 grains
Water to make 1 gallon

I think there is a Kodak lith developer with these ingredients but kept in two parts until use. D-8 maybe?
 
 
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