Catechol and Hydroquinone Stain

Early Tanning developer ( "Developing", CI Jacobson 1948 p162) used catechol, more recently it is used eg in the Pyrocat series and in Obsidian Aqua (Jay deFehr).
I used Obsidian Aqua-type with the specified catechol vs the same with catechol replaced by hydroquinone.

Demin water.........................40ml
Sodium metabisulfite.............0.2g
Catechol (or hydroquinone)....2.5g
Demin water to.....................50ml
Dilute 1:100 with 6.7g/L Potassium Carbonate solution.
Develop Tri-X (spare 2008 date) 12min 20C Agitate 10s/min

Attachment shows both catechol and hydroquinone produce stain.
Bleaching and fixing a negative from the hydroquinone developer showed a relief image indicating tanning.

Prints were made from scans processed identically.
(1) Neither was particularly fine grain
(2) Hydroquinone gives more grain and less sharpness than catechol.

This one experiment provisionally suggests that (2) is the reason why catechol is used in preference to hydroquinone in practice.
It is also a lot more soluble than hydroquinone.

nice work, its always nice to see other peoples experiment with "new" developers.

A couple years ago I took the three basic Pyrocat (HDC, MC, and PC) recipes and just for fun used HQ in place of catechol at 50g/L. I tested all three out on 35mm film and all three HQ versions stained a red-brown stain, where as the catechol appears more brown-black, except with the -MC version which looks slightly more red to me. When printed to 5x7 it was hard for me to tell the difference between the catechol and the HQ versions. I did like the grain of the HQ-PC version which like the Pyrocat version has slightly larger grain. If there is interest, I will look for my HQ negs next time I go to the darkroom and post them.

You should have a reference to show the base color and show that the stain is real and not part of the dye used for prevention of light piping.

PE

ritternathan said:

A couple years ago I took the three basic Pyrocat (HDC, MC, and PC) recipes and just for fun used HQ in place of catechol at 50g/L. I tested all three out on 35mm film and all three HQ versions stained a red-brown stain, where as the catechol appears more brown-black, except with the -MC version which looks slightly more red to me. When printed to 5x7 it was hard for me to tell the difference between the catechol and the HQ versions. I did like the grain of the HQ-PC version which like the Pyrocat version has slightly larger grain. If there is interest, I will look for my HQ negs next time I go to the darkroom and post them.

Click to expand...

Perhaps the HQ variation of pyrocat has smaller grain than the mix I tested. Others have commented on this variation.
Tom Hoskinsonthere was a url link here which no longer exists)
Mehmet Kismetthere was a url link here which no longer exists)
The hydroquinone version is apparently slightly less active and more contrasty in highlights than the catechol version.

I might try a different approach later this week if I get time. I use Ilford IT-8 toner occasionally it's a Dichromate re-halogenating bleach followed by a simple Pyrocatehin developer. I'll try a similar Hydroquinone version.

Ian

Michael R 1974 said:

I am puzzled by the picture of the negatives. Since these are the same type of film, and the brown colour on the HQ sample is visible everywhere (ie including unexposed areas), if that is indeed HQ stain there appears to be a high level of non-imagewise stain/fog stain on that sample. I'd also suggest using fresh film for these kinds of tests.

Click to expand...

Another way of interpreting this is to propose that hydroquinone requires a higher sulfite content than catechol to prevent overall non-image stain. This is the value of keeping all but one variable constant in a series of experiments.

It would be interesting to see a series of experiments where the amount of sulfite is increased until the overall stain no longer occurs. This of course would also reduce the amount of image stain. This would be in line with what Michael and I have said that hydroquinone produces less image stain than catechol.

The oxidation colour of Hydroquinone in a developer is a reddish Brown, Pyrocatechin - Blue/Green. When I use IT-8 toner if the re-developer has turned blue-green then it stains the emulsion, and paper base with FB papers. IT-8 gives olive warm tones.

Ian

I added a reference from the same strip if out of date Tri-X, developed in Perceptol 1+0.There is fog.

Higher perceived sharpness can come from local restraining effects, i.e. a strongly exposed area prevents development in a neighbouring weakly exposed area and thereby increases local contrast. Typical examples used in practice are local exhaustion effects, or DIR couplers in colour processing. Hydroquinone, one the other hand, creates infectious development if its oxidized product is not scavenged. By simple extrapolation (enhanced activity equals negative restraint) this could be the cause of less sharpness, exactly what you saw in your tests.

Since Michael mentioned differences in activity: the pKa1 and pKa2 values for HQ and Catechol are tabulated in James, The Theory of the Photographic Process, 4th edition: 9.91 and 11.56 for HQ, and 9.25 and 12.37 for Catechol. While this would suggest higher activity of Catechol at pH < 11, this may change at pH > 11, and it is counteracted by Catechol's lower reduction potential at pH=0 (-E0 = -0.760 for Catechol vs. -0.699 for HQ). Activity is different, and the difference is not the same at different pH values. Since we don't know the pH (but assume it is somewhere between 10.5 and 11.5, given the compos, we can't really tell which version is more active. Higher fog of the HQ version suggests that HQ is more active.

Since we can safely assume that Jay did some optimization to his recipe, there is a good chance that an optimized HQ version could perform better than the results from simple substitution would suggest. Higher Dmin level could at least explain some of the higher granularity of the HQ sample, and different levels of Metabisulfite could strike a balance between stain and sharpness.

Conclusion: interesting test, but given the much easier availability of HQ it doesn't fully explain the lack of staining dev recipes based on HQ. I still wonder how stable HQ's stain is over time, especially compared to Catechol and Pyrogallol.

I also noticed increased fog when I used the Pyrocat recipe with HQ and used the standard B solution of 750g/L Pot. Carbonate at 1:1:100. So I tried using 200g/L of Sodium Carbonate at 1:1:100 and got a little less fog. I then tried using 99% TEA as a B for the HQ pyrocat recipe at 1:1:100 and got much less stain. Anyone have an idea of what an ideal ph would be for a HQ version of Pyrocat or at least a starting point?

Noting the comments that HQ might be acting like a lith developer and that it gives increased fog, I made up a version using metaborate Part B.
This is a copy of PMK Pyro with hydroquinone replacing pyrogallol.

HQ-PMK
Part A
Demin water...........................90ml
Metol.......................................0.5g
Sodium metabisulfite.................1.0g
Hydroquinone............................5.0g
Demin water to.........................100ml

Part B
Demin water............................70ml
Sodium metaborate (Kodalk)......30g
Demin water to.........................100ml (both parts dissolve on gentle heating with stirring)

For use mix 2 parts A + 2 parts B to 100 parts water.(pH by paper ~10)
I developed the same film as before, for the PMK Pyro time.
Now the grain is much reduced compared to the result reported above using carbonate.
I don't think the inventor of PMK Pyro discussed the reason for not using hydroquinone.

I developed the former Agfaphoto APX 100 using HQ-PMK and 510 Pyro (attachments).
Lighting conditions were different and grain cannot be seen in these computer images but examination of prints shows grain from 510 Pyro to be finer.
I daresay because it has the lowest pH of all Pyro developers 510 Pyro is probably gives the finest grain out of all of them.

Alan, contrast does not look the same.

PE

the captea is a waste of tea. You still require a heavy alkali to start the catechol. just make some hypercat and add the phenidone.....that's what I do. Works great.

The pptea is basically 510Pyro without some AA to preserve.




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Looking for fine grain, the lower pH HQ-510 Pyro was tested vs 510 Pyro, using the same 2008 expired Tri-X.

HQ-510 Pyro
Triethanolamine................85ml
Ascorbic Acid......................5g
Hydroquinone....................10g
Phenidone.........................0.25g
Triethanolamine to.............100ml
This was heated to 200F in a stainless steel pot on a hotplate using a meat thermometer and stirring with a spoon.
Caution, flammable.
Dilute 1:100 for use.

Time required to develop in HQ-510 Pyro was about double that for 510 Pyro.
The grain was not quite as fine as that obtained using 510 Pyro itself and barely distinguishable from HQ-PMK Pyro.
Attachment shows the stain using HQ decreased with falling pH.
510 Pyro itself gave the finest grain of the combinations tested. This may be because the pyrogallol still stains at the pH of TEA.

The AA is used as a preservative. I wonder if it work better without it entirely.

Michael R 1974 said:

...

I am puzzled by the picture of the negatives. Since these are the same type of film, and the brown colour on the HQ sample is visible everywhere (ie including unexposed areas), if that is indeed HQ stain there appears to be a high level of non-imagewise stain/fog stain on that sample. I'd also suggest using fresh film for these kinds of tests.

Click to expand...

All staining developers that I know of show a combination of general stain (everywhere) and image stain (proportional to the image density). Here, the general stain for the hydroquinone developer is more apparent. But the stain is dependent on a number of things, including pH and sulfite concentration, and is different for different developing agents.

I did a test, in another thread, and made a hydroquineone + metol in tea. It did not stain. In the example here, I suspect it's just a normal QP or a AP development action. Until the silver is bleached and removed, we will not know.

Alan Johnson said:

Perhaps the HQ variation of pyrocat has smaller grain than the mix I tested. Others have commented on this variation.
Tom Hoskinsonthere was a url link here which no longer exists)
Mehmet Kismetthere was a url link here which no longer exists)
The hydroquinone version is apparently slightly less active and more contrasty in highlights than the catechol version.

Click to expand...

I don't want to derail this interesting thread, but I'm curious if there is a theoretical or practical reason Mehmet keeps the original quantity of KBr (1 g) unchanged in his recipe, which is essentially a halved variation of Pyrocat-HD in all other respects (except the substitution of Q).

Results for the relief image (tanning) after I bleached and fixed the negatives:
OA type .........(Catechol-carbonate)................strong relief image.........pH~11
HQ-OA type..., (Hydroquinone-carbonate).........moderate......................pH~11
HQ-PMK..........(Hydroquinone-metaborate).......faint.............................pH~10
510 Pyro.........(Pyrocatechin-TEA)..................moderate to strong..........pH~9
HQ-510 Pyro....(Hydroquinone-TEA).................none detected.................pH~9

Conclusion-Hydroquinone tans less than Catechol at pH~11 and the degree of hydroquinone tanning falls with pH till not detected at pH ~9.
510 Pyro itself still tans quite strongly at pH ~9.

One has to be careful not to try to compare apples and oranges. The presence of any other developing agent in a developer really complicates the question. One has to stay focused on a developer containing a single developing agent either catechol or hydroquinone. In addition remember that ascorbate is a developing agent besides being a preservative. Also pyrogallol is very different in its chemistry from either hydroquinone or catechol.

I finished investigating hydroquinone, but since the subject is raised, I suggest that pyrogallol may first ionise, then donate an electron via phenidone to develop a silver ion and produce a phenoxy type free radical, just like hydroquinone.
In support of this, here it is suggested that only two of its -OH groups are oxidized, giving a quinone, again just like hydroquinone.This is what would do the crosslinking in tanning.
http://chemistry.stackexchange.com/...ss-alkaline-solution-of-pyrogallol-and-why-do