Help with some basic chemistry (theory) on developers

Alan Johnson · Sep 13, 2018

There is a long discussion of hydroxyhydroquinone formation in absence of sulfite by Mason c p70.
"LuValle and Goldberg ,,,,,,,,,,,,,,also suggest that hydroxyhydroquinone is the catalyst in infectious development."
So you are on to the chemistry of lith development here.

Photo Engineer · Sep 13, 2018

Well, just to complicate matters, here is something I have never found in a textbook but is quite real and quite important. Quinhydrone can form in HQ itself and in HQ developers. It forms as green needles when solid and tints the solution brownish green in liquid form. It has an odd odor that is very strong. It can affect developer activity.

As for helping, I don't feel as if I've given much but I'm willing to continue here giving support and any help I can.

I can say that there are surprising twists and turns in any developer design. Earlier, someone asked why so little Sulfite is used in color developers. It is because it is a competing coupler of a sort and undergoes the same reaction with the CD agent when the PPD is oxidized that HQ does when it is oxidized. The monosulfonate of the oxidized color developer forms. However, in this case, the monosulfonate is inactive.

PE

Anon Ymous · Sep 13, 2018

Photo Engineer said:
Well, just to complicate matters, here is something I have never found in a textbook but is quite real and quite important. Quinhydrone can form in HQ itself and in HQ developers. It forms as green needles when solid and tints the solution brownish green in liquid form. It has an odd odor that is very strong. It can affect developer activity...

Quinhydrone is a 1:1 complex of hydroquinone with quinone. I assume it can form when both compounds exist in solution. I also assume that quinone is the thing that makes it smell, although a sample I have doesn't have much of a smell. The solution it came from on the other hand... it reeked!

elerion · Sep 14, 2018

Quinhydrone is another compound, I didn't know about. It is not quinone, but similar to two quinone molecules joined by H?

About the reaction of quinone to HQ:
2 C6H4O2 + H2O -> C6H4(OH)2 + C6H3(OH)O2

I suppose this doesn't mean HQ can be "recharged", because being optimistic, 2 moles of oxidized HQ turns in 1 mole of HQ (and only in high enough pH solution), so it will end up being consumed.

Really, I'm interested in HQ only from a theory point of view, because there's more information on it than other agents, and helps to learn and understand some basic concepts. It is very difficult to get, and it will probably (if not already) prohibited in Europe.

Yesterday the chemist of a local shop told me that it is already imposible to buy phenidone in Spain, that he would have to buy it from an international distributor, because, on his own words, it is a dangerous chemical (?), and they have trouble with authorities. Phenidone. You can bet about HQ,... It doesn't make much sense, as they do sell NaOH and silver nitrate (which I always thought was more toxic than most developers).

Rudeofus · Sep 14, 2018

You can get HQ and Phenidone from Fototechnik Suvatlar in Germany. Shipping may be more expensive that getting it locally, but trust me: 500g of HQ and 25g of Phenidone last a loooong time.

The problem with Phenidone is not so much that it's dangerous, but that it has no application outside photography, so more and more distributors take it out of their inventory.

elerion · Sep 14, 2018

Yes, I knew that one and also disactis, in France. Shiping cost is almost 20 euros.
About HQ, from now on, I'd rather use phenidone and ascorbic acid developers. I preffer to use the safests chemical possible. And I like xtol like developers a lot (along with Rodinal,which I know is on the same league as HQ or metol). Ther're lots of good phenidone/ascorbic formulas out there, and small quantities of p-aminophenol for some specific works is quite enough for me. For one shot we can even leave out sodium sulfite, sequestring agents,... and many formulas don't even need KBr or KI.
I'm finishing my B&W paper developer (Ilford, MQ type), and I bought an ascorbic one (Nautol eco) to replace it, which I didn't test yet.

GLS · Sep 14, 2018

elerion said:
Quinhydrone is another compound, I didn't know about. It is not quinone, but similar to two quinone molecules joined by H?

It is an adduct (or complex) of hydroquinone and benzoquinone. The two components are not bonded together in the usual sense, but are stabilised by hydrogen bonding. Such species qualify as distinct compounds.

Anon Ymous · Sep 14, 2018

Rudeofus said:
You can get HQ and Phenidone from Fototechnik Suvatlar in Germany. Shipping may be more expensive that getting it locally, but trust me: 500g of HQ and 25g of Phenidone last a loooong time...

Surprisingly, his latest catalogue doesn't list Hydroquinone as far as I can tell. It doesn't list potassium dichromate either, but it's a restricted substance. Does that mean that Hydroquinone has been restricted as well?

Rudeofus · Sep 14, 2018

Anon Ymous said:
Surprisingly, his latest catalogue doesn't list Hydroquinone as far as I can tell. It doesn't list potassium dichromate either, but it's a restricted substance. Does that mean that Hydroquinone has been restricted as well?

This definitely does surprise me, since HQ is still offered by SIlverprint and by Keten, both of which are on EU grounds. I'd ask Saban Suvatlar for a quote on HQ, the price list cryptically states something I would loosely translate as "further compounds and larger amounts per RFQ only".

elerion · Sep 15, 2018

You can still buy HQ at disactis. 100g, 9,28 €. There's only this warning:
"CAUTION: This product is regulated. In order to limit its use solely to Photographic use, it is not available for single purchase. Only orders that are also made up of other products demonstrating the use for which it is intended, or the justification of your activity in this area are therefore accepted if you only need this reference. Otherwise, orders will be canceled and fully refunded."

Potassium dichromate is already banned in Europe AFAIK.

It is a matter of time that more chemicals will follow.
Todays's trend seem to be that everything should be fool-proof.
I think this initiatives are good in essence, because lots of people are just not prepared to handle certain situations (and sometimes affect others too, like these people who drive their cars at 200 km/h+ and upload videos to YouTube; deadly threats; of course this is a totally different matter, just an example of thoughtlessness), but there will be people who are totally qualified to do and buy certain things. We will see.

GLS · Sep 15, 2018

Rudeofus said:
since HQ is still offered by SIlverprint

That's a complete ripoff. You can buy the same amount directly from Sigma for a third of the price. Fisher are even cheaper.

Rudeofus · Sep 15, 2018

GLS said:
That's a complete ripoff. You can buy the same amount directly from Sigma for a third of the price. Fisher are even cheaper.

It is quite obvious from the product image, that Silverprint resells HQ from Sigma Aldrich, however, that latter won't even sell Dihydrogenmonoxide to non-commercial outfits. As normal citizens we have to put up with a stiff markup, and I'd warrant a guess that part of that money goes into "extreme vetting" of their potential customers.

That's the problem with any hobby relying on raw chemical compounds: you have to jump through burning hoops to get trivial compounds, which are a lot more benign than random cleaning agents or the contents of your car battery, both of which are sold to just about anyone.

GLS · Sep 15, 2018

Rudeofus said:
It is quite obvious from the product image, that Silverprint resells HQ from Sigma Aldrich, however, that latter won't even sell Dihydrogenmonoxide to non-commercial outfits

Oh I know. I just wasn't aware that there was so much price gouging going on with resellers. I'm not sure how much meaningful vetting of customers they will be able to do; rather I suspect some of the markup goes towards reseller's insurance.

I'm in the lucky position to be able to buy whatever I might want from chemical suppliers through work, should I ever feel the need to start mixing my own developers.

MattKing · Sep 15, 2018

GLS said:
Oh I know. I just wasn't aware that there was so much price gouging going on with resellers. I'm not sure how much meaningful vetting of customers they will be able to do; rather I suspect some of the markup goes towards reseller's insurance.

I'm in the lucky position to be able to buy whatever I might want from chemical suppliers through work, should I ever feel the need to start mixing my own developers.

It is only "gouging" if the net profit enjoyed by the retailer is overly high.
I don't know about GLS, but I have observed generally that very few people on this and other sites have a good idea what it costs to run a retail sales business!

elerion · Sep 20, 2018

This one is not really chemistry related, but I reached to this question while reading about it, and right now I cannot find an answer. Sure, it must be evident.
Facts:
- Development accelerates the process of metallic silver formation. It mainly reduces those grains which already contain a few metallic silver atoms, as result of ionization of silver halide due to light exposure, and combination with mobile silver cations. Latent image is not visible.
- Enough exposure (i.e, days long) should make visible the latent image, as silver specks continue to grow due to exposure.

Why a strip of strongly day light exposed film, after being fixed, ends up almost transparent? Would't there be enough metallic silver due to exposure, to develop non negligible density?

Rudeofus · Sep 20, 2018

It depends on what you call "strongly day light exposed" film. Remember that fixer was invented long before there was developer - at the onset of photography glass plates were exposed long enough to get visible printout silver.

Photographic development is a massive amplification process, a few metallic silver atoms clustered together are enough to render a whole grain developable. A cubic meter of AgBr weighs about 6.5 t, this means a typical AgBr grain of one µm3 weighs about 6500 * 10-18 kg = 6.5 * 10-15 kg = 34,6 * 10-15 mol = 2 * 1010 silver and bromide ions. Developing such a grain means amplification of these few silver atoms by about a billion!

Photo Engineer · Sep 20, 2018

Silver metal formed by printout due to overexposure is very fine. It shows up by contrast with the Silver Halide before a coating is fixed because internal reflections amplify the differences just as they do on paper. Thus the image seems to have higher visual contrast until the background Silver Halide is fixed out.

Also, the fixer dissolves some of that Silver metal because it is so finely divided. You often see loss of density in the toe region of any negative or print for the same reason.

PE

GLS · Sep 20, 2018

Photo Engineer said:
Also, the fixer dissolves some of that Silver metal because it is so finely divided. You often see loss of density in the toe region of any negative or print for the same reason.

I've wondered about this before from a chemistry perspective.

Does that mean that if you fix long enough you could theoretically obliterate the deepest shadow detail in a neg?

Photo Engineer · Sep 20, 2018

Theoretically, yes. It is the acid that is the main culprit. Alkaline fixers or neutral fixers avoid this to some extent.

PE

Help with some basic chemistry (theory) on developers

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