Why Pyrol rather than hydroquinone?

gainer · Jun 11, 2005

I hate it when people call me Mr. Gainer. It makes me feel older than I am, and that's not easy to do.

Of course, I know people are using lith developers for other than lithography. That's a misnomer anyway. Who uses rocks? But if it's not fundamentally a lith developer, how can one say "I used a lith developer for a full scale landscape."? So what makes a lith developer a lith developer? What do you mean by "lithing" if not high contrast and infectious development?

Now, if a developer that produces only two levels of density on film designed for lithography is applied to HP5+ or 400TX, say, we don't expect only two density levels, but we can't get the effect of using a lith developer without using a developer that could be used in lithography. Or am I missing something?

dancqu · Jun 11, 2005

gainer said:
"I hate it when people call me Mr. Gainer. It makes me feel
older than I am, and that's not easy to do."

OK, I'll go corporate. P. G. the matter is not at all complex and
we are not caught in a semantics quick sand. We are both talking
about HQ based developers which produce infectious development.
So, the subject is lith developers.

Full scale pictorial results require that the exposure of the paper,
the lith developer, and process times be much changed; much longer
exposures, much diluted developer, much longer development times.

I'll point out that Ortho Line and Halftone Film, lith film, is being
processed to yield full scale, pictorial, results.

"So what makes a lith developer a lith developer? What do you
mean by "lithing" if not high contrast and infectious development?"

Hydroquinone is the only agent, I'm quite sure, which will produce
infectious development. The printing industry requires high contrast
so they compound and use accordingly.

" ... but we can't get the effect of using a lith developer without
using a developer that could be used in lithography. Or am
I missing something?"

I think that those who make full scale prints might use
formulations which do infectiously develop but would not be
of use to the printing industry.

Usually APUG lith printing is discussed in the Alternative Processes
Group. A fellow by the name Tim Rudman has a book out on the
subject. Many more sources of information exist. Dan

gainer · Jun 11, 2005

dancqu said:
"Hydroquinone is the only agent, I'm quite sure, which will produce
infectious development. The printing industry requires high contrast
so they compound and use accordingly."

Besides catechol and pyrogallol and others like them, I'm sure you meant to say.

I don't remember how the subject got switched to lithography or its alternate uses. I do remember that I made the statement that a developer composed of hydroquinone and TEA would probably not make a good lith developer. I have a developer composed of phenidone, hydroquinone and sulfite that I know will not make a good lith developer. Whether you want to use a lith developer for its originally intended purpose or something else does not IMHO keep it from being a lith developer. Conversely, whether you want to use a developer intended for continuous tone reproduction or not does not make it a lith developer. So what? In any case, I know that a hydroquinone developer without sulfite will produce a stained image.

dancqu · Jun 12, 2005

gainer said:
dancqu said:

""Hydroquinone is the only agent, I'm quite sure, which will produce
infectious development. The printing industry requires high contrast
so they compound and use accordingly.""

"Besides catechol and pyrogallol and others like
them, I'm sure you meant to say."

I'll go a little farther out on the limb. Hydroquinone IS THE
ONLY developing agent which will produce infectious development.
Of course that is inviting news to the contrary BUT I've looked at
and studied a lot of lith developer formulas and have never seen
any other agent but hydroquinone as the developing agent. Dan

Click to expand...

Tom Hoskinson · Jun 12, 2005

dancqu said:
gainer said:

dancqu said:

""Hydroquinone is the only agent, I'm quite sure, which will produce
infectious development. The printing industry requires high contrast
so they compound and use accordingly.""

"Besides catechol and pyrogallol and others like
them, I'm sure you meant to say."

I'll go a little farther out on the limb. Hydroquinone IS THE
ONLY developing agent which will produce infectious development.
Of course that is inviting news to the contrary BUT I've looked at
and studied a lot of lith developer formulas and have never seen
any other agent but hydroquinone as the developing agent. Dan

Click to expand...

------------------

Well, there is evidence to the contrary.

Regarding Infectious Development, take a look at:
Appreciating Rodinal: By Ed Buffaloe

http://unblinkingeye.com/Articles/Rodinal/rodinal.html

Quoting a statement by Pat Gainer in the referenced Ed Buffaloe article:
In a manner of speaking, all development is infectious. It begins with an invisible latent image in only a molecule or two in a crystal and spreads to the rest of the crystal. Sulfite inhibits this growth. It appears that ascorbates also do so.

-------------

Here is another interesting looking abstract of a paper on infectious development involving ascorbates found at:

http://www.dic.co.jp/eng/rd/tech/rep0401/

Title: Mechanistic Studies of a New Nucleated Infectious Development Using Pyridinium Salts: Nucleation of Silver Halide Grains by Dihydropyridines

Naoki OBI, Jun TAKEUCHI, Yasuhiko KOJIMA, Yasuo SHIGEMITSU, A. Gary DIFRANCESCO and Richard K. HAILSTONE

"Photographic properties of 1-benzyl-1,4-dihydronicotinamide (BNAH) are studied for better understanding of the mechanism of the production of high contrast by the infectious development which is induced by the combination of a pyridinium salt and Metol-ascorbate developer. Treatment of silver bromide emulsion or silver chlorobromo emulsion by BNAH and redox buffer followed by development gave high fog density. It has been suggested that the oxidation product of BNAH by redox buffer nucleates silver halide grains and makes them developable. Results support the hypothesis that dihydropyridine works as an intermediate in the production of high contrast by the infectious development in the presence of a pyridinium salt."

------------------------------

An interesting Infectious Development Patent (3M) can be found at:

http://gauss.ffii.org/PatentView/EP182293

Abstract: A process is disclosed for forming a high-contrast photographic image by developing a silver halide photographic element, including at least a silver halide emulsion layer, with an aqueous alkaline developing solution containing a dihydroxybenzene developing agent, a superadditive developing agent and an antioxidant at a pH of less than 12 in the presence of a hydrazine compound, an organic antifogging and contrast promoting agent selected within the class including a benzotriazole compound and a benzimidazole compound and a non polymeric hydroxymethylidyne group containing compound of formula: wherein R1 and R2 each independently represent a hydrogen atom, an aliphatic group, an aromatic group, a heterocyclic group, or R1 and R2 together complete a non aromatic cyclic group.

This patent description includes a long list of dihydroxybenzene developing agents that will work, and calls out hydroquinone as the dihydroxybenzene developing agent of the author's choice.

Click to expand...

dancqu · Jun 12, 2005

Tom Hoskinson said:
All that you've included in your post will take some study.
From reading your last line, below, I'd have been more accurate
to have mentioned the dihydroxybenzene compounds rather
than hydroquinone. It is likely that hydroquinone is the
only agent used in lith formulas for reasons which
make impractable the use of other agents.

I may have been only technically too far out on the limb. Dan

"This patent description includes a long list of dihydroxybenzene
developing agents that will work, and calls out hydroquinone as
the dihydroxybenzene developing agent of the author's choice."

sanking · Jun 12, 2005

dancqu said:
Tom Hoskinson said:

It is likely that hydroquinone is the
only agent used in lith formulas for reasons which
make impractable the use of other agents.
Dan

Click to expand...

Why is that likely? Off hand I can not think of any reason why the other reducers mentioned in this thread, such as pyrogallol and pyrocatechin, would be any more impractical in use than hydroquinone for this particular application?

Specifically, what is it about infectious development that can be achieved with hydroquinone and not with pyrogallol and pyrocatechin? And why do you believe that to be the case, other than the fact that the formulas you have studied all contain hydroquinone? Have you actually tested another reducer for this type of development?

Sandy

dancqu · Jun 13, 2005

sanking said:
"Why is that likely? Off hand I can not think of any reason why
the other reducers mentioned in this thread, such as pyrogallol
and pyrocatechin, would be any more impractical in use than
hydroquinone for this particular application?"

The 3M patent Mr. Tom Hoskinson mentioned in one of his posts
is suggested reading. The agent of choice was hydroquinone.
Perhaps I should have said less practical or less suitable in
regards other agents.

"Specifically, what is it about infectious development that
can be achieved with hydroquinone and not with pyrogallol
and pyrocatechin?"

I've no idea. I've used only hydroquinone as an infectious
developing agent. Are pyrogallol and pyrocatechin members
of the dihydroxybenzene group refered to in the 3M patent?

"And why do you believe that to be the case, other
than the fact that the formulas you have studied all contain
hydroquinone?"

All the formulas at Unblinking Eye and 24 X 30 contain
hydroquinone. That last site may be reached by entering
at Google, "walls normal hydroquinone" . Dan

Bob Carnie · Jun 13, 2005

Dan
I am doing quite a bit of lith printing in fact started in 1997 and it is part of my weekly production.
I hesitate to enter this discussion as my background is entirely practical with no scientific credentials. Though I do make a living making lith prints.
It seems to me you are trying to come up with a good workable formulation for lith printing. My comments to you in other posts (different threads) were that Champion Nova Lith is the best mix I have used.I have tried some of the formulas from unblinking eye as well I have used the kodak lith chemicals. All of these pale by comparison to Champion.
I have noticed that with Champion when mixing the b with the a there is a milky white formation happening . this does not happen with any of the other combinations that I have had mixed up.I bought 10 5 gallon mixes of Champion as I rely on this developer working every day consistantly. If you would be interested I would send you some a and b to test with the mixes you are using and see if there is a difference.
If you have a formula that makes the blacks pop after 3 minutes and gives the creamy highlights then you are on to a good thing. But I know kodak mix will not do this as well as two of the formulas posted on unblinking eye. They work but nowhere near Champion.

Helen B · Jun 13, 2005

Sandy enquired, perhaps rhetorically:

"Specifically, what is it about infectious development that can be achieved with hydroquinone and not with pyrogallol and pyrocatechin?"

Is it that semiquinone is sufficiently active to cause infectious development, and that semiquinone is formed by the reaction between hydroquinone and quinone (as long as there is no more than a very low concentration of sulphite ions and in the presence of a necessary small amount of bromide ions)?

But on the other hand... fogging of the adjacent grains can be accomplished by other substances, including the reaction product of hydrazine (for example) and the oxidised developer. The result of fogging adjacent grains is similar, but not identical, to infectious development.

The distinction between infectious development and fogging is that infectious development refers to the development of grains with latent sub-image centres while fogging refers to the development of unexposed grains.

How does that sound? I'm not suggesting that semiquinone is the only substance capable of causing infectious development. I don't know the answer to that question. I'm not sure that I know any answers really.

Best,
Helen

sanking · Jun 13, 2005

dancqu said:
"And why do you believe that to be the case, other
than the fact that the formulas you have studied all contain
hydroquinone?"

All the formulas at Unblinking Eye and 24 X 30 contain
hydroquinone. That last site may be reached by entering
at Google, "walls normal hydroquinone" . Dan

I understand that all of the formulas contain hydroquinone, but that in and for itself does not mean that other reducers could not also be used. Lith printing is a fairly new technique and it would be expected that most people working with it are simply adopting the few formulas that have to this point been recommended. I have no idea if procatechin or pyrogallol would work as well, or better, than hydroquinone, but unless someone has actually tried these reducers and found that they don't work I would certainly withold my own judgement about their usefullness.

Sandy

Tom Hoskinson · Jun 13, 2005

It seems to me that the articles and patent I cited in my previous post either imply or state that several developing agents are capable of infectious development and are also useful in Lithographic development.

Several of these are dihydroxybenzene developing agents (including, but not limited to hydroquinone) and several are not.

It would seem to me that testing is indeed indicated before any judgements are made about usefulness or lack thereof of any of these developing agents in lithographic applications.

Helen B · Jun 13, 2005

Reading the articles and patent quoted by Tom made me think that 'infectious development' is applied with a more general meaning than the specific one I used in my attempt to reconcile the two viewpoints (there being two different mechanisms of lithographic development, not one. One of those mechanisms appears to be rather special, and one does not).

Best,
Helen

gainer · Jun 13, 2005

I suspect that the fact that hydroquinone WILL do the job in a properly formulated developer and is less expensive (at least for me) than others that would also do the job is the real reason it is used in commercial developers. That is not a pronouncement, just an observation.

sanking · Jun 14, 2005

gainer said:
dancqu said:

I don't remember how the subject got switched to lithography or its alternate uses.

Click to expand...

Well, just for the record here is how it happened. For whatever it is worth.

"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"

Sandy

dancqu · Jun 16, 2005

Kirk Keyes said:
Perhaps the high density of the lith image
makes the stain not noticable.

Just what I was thinking possible. Many years ago I did
process camera work and half tone processing. I was not
looking for color then but on reflection do not recall any.
Those little dots are small and/or compressed and all
very dense.

The little lith printing I've done shows the dense portions
to be black, warm at best, while any less dense areas shade
from light tans to very dark browns; at least with my
homebrew lith. Dan

dancqu · Jun 16, 2005

sanking said:
"For whatever it is worth."

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.

I've given that above some additional thought. On reflection,
when working with my lith surprise brew, I saw that the
image tanned brown as it emerged. After several minutes of
slow increase in density a rather fast increase took place.

Hydroquinone initiates the reduction of the silver halides and
the semiquinone is produced. The semiquinone is consumed
by the gelatin, that being tanned. Hydroquinone MAY be
regenerated at that time. Quinone though, necessary
for infectious development, is NOT produced.

After most of the tanning has been done the semiquinone is
free to oxidize to the quinone and infectious development
takes off. All that with low sulfite levels.

But what if sulfite levels are high? Nothing happens; perhaps
a faint image. Interesting. By that I'd conclude that more
than a very little sulfite will maintain a regenerated
hydroquinone.

Likely the level of sulfite mentioned, 2 grams per liter, may
vary some and one still expect a tanned, lithed print. Dan

Why Pyrol rather than hydroquinone?

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