Metol / HQ ratio

[David Lyga]

For negatives, there are developers capable of more than adequate contrast that contain NO hydroquinone (D-23, D-25).

For negatives, there are developers capable of more than adequate contrast that contain the same amount of each developer component (DK-50).

For negatives, there are developers capable of more than adequate contrast that contain more than twice as much hydroquinone as metol (D-76).

What is hydroquinone supposed to do? It does increase contrast a bit but this increase is not needed with standard negative material. Of course, that increase in HQ would be appropriate to have for paper developers. But ALL of the above formulae are fully capable of giving negatives that have all the contrast wanted (unless you are doing 'lith').

Another argument is that hydroquinone rejuvenates metol. That might benefit the developer's longevity.

But what else? Honestly, I see no other benefit to adding HQ to the metol for standard negative development.

Tell me where I err. - David Lyga

 

[Rudeofus]

HQ appears to be quite a bit cheaper than Metol. Also remember that Metol had PPD impurities in the past which caused it to trigger allergic reactions. It's not sure whether HQ actually improves anything photographically, Grant Haist reformulated D-76 to use Metol only.

 

[Alan Johnson]

The oxidation product of metol adsorbed on silver halide grains is not a developer.
It is probable that it is removed more rapidly by regeneration with hydroquinone than it is by reaction with sulfite.
So adding hydroquinone shortens the development time and made it preferable for use in the early movie industry I daresay.

 

[RPC]

I feel it is the case that hydroquinone is not really needed. AAMOF I avoid it due to the resulting activity change it can cause over time and use only hydroquinone-free developers.

 

[Ian Grant]

HQ appears to be quite a bit cheaper than Metol. Also remember that Metol had PPD impurities in the past which caused it to trigger allergic reactions. It's not sure whether HQ actually improves anything photographically, Grant Haist reformulated D-76 to use Metol only.

Grant Haist didn't reformulate D76 to use just Metol, see (there was a url link here which no longer exists)

Ian

 

[Rudeofus]

Grant Haist didn't reformulate D76 to use just Metol, see (there was a url link here which no longer exists)

This developer you quote here is basically D-76 without the HQ, but should behave quite differently from the latter. Grant Haist, on the other side, crafted a D-76 version without the HQ, which he claimed behaves the same as D-76. It's called D-76H and uses 2.5 g/l Metol instead of the 2 g/l used in plain D-76 in order to replace the 5 g/l HQ.

 

[Ian Grant]

This developer you quote here is basically D-76 without the HQ, but should behave quite differently from the latter. Grant Haist, on the other side, crafted a D-76 version without the HQ, which he claimed behaves the same as D-76. It's called D-76H and uses 2.5 g/l Metol instead of the 2 g/l used in plain D-76 in order to replace the 5 g/l HQ.

Kodak D76h does indeed contains 2.5g Metol but also contains Hydroquinone, and had nothing to do with Haqist. Below is Eastman Kodak's D76h (D76variant)

D76h Fine Grain Film Developer

Metol 2.5 g
Sodium Sulphite (anh) 100 g
Hydroquinone 5 g
Borax 2 g
Boric acid 15 g
Water to 1 litre

All these formulae came from the same team that formulated the first Eastman Kodak Research Fine Grain developer, D76 and all the variants, d23 & D25, DK20 etc. Haist had no input it, he suggested that a version of D76 with only Metol was possible to an author in a conversation and gave a suggestion.

Ian

 

[Gerald C Koch]

Kodak D76h does indeed contains 2.5g Metol but also contains Hydroquinone, and had nothing to do with Haqist. Below is Eastman Kodak's D76h (D76variant)

D76h Fine Grain Film Developer

Metol 2.5 g
Sodium Sulphite (anh) 100 g
Hydroquinone 5 g
Borax 2 g
Boric acid 15 g
Water to 1 litre

All these formulae came from the same team that formulated the first Eastman Kodak Research Fine Grain developer, D76 and all the variants, d23 & D25, DK20 etc. Haist had no input it, he suggested that a version of D76 with only Metol was possible to an author in a conversation and gave a suggestion.

Ian

Yes, there is a D-76h and while Haist did not originate the designation D-76H it has been used for his recommended variant. So in this case the lack or presence of a capital 'H' is important.

 

[Gerald C Koch]

Metol and hydroquinone are a super-additive combination. Therefor the rate of development is enhanced. The is important for a low pH MQ developer like D-76 to avoid long development times. There is an optimum ratio for the two developing agents. For an MQ developer this is approximately 1 part metol to 6 parts hydroquinone. This is discussed in Mason* which contains a 'U' shaped graph of development time vs the MQ ratio. The low point occurs at 1:6 w/w.

* While not as up to date as Haist's magnum opus LFA Mason Photographic Processing Chemistry is still a very useful book. It should be on the library shelf of anyone interested in photographic chemistry.

 

[pdeeh]

 

[Gerald C Koch]

View attachment 171791

Glad you posted the graph. The one in Mason is very small and I believe gives a simple w/w ratio.

 

[pdeeh]

that is straight from Mason, 2nd Ed, p.119
He has a similar graph on p.120 for Metol/Phenidone.

I learned a huge amount from that book, even thought I could understand only about 20% of it.
For anyone with a chemistry degree, no problem.

 

[grahamp]

The darkroom Cookbook covers super-additivity. The relevant text is at https://books.google.com/books?id=B...nepage&q=hydroquinone superadditivity&f=false (Google, if the link survives).

On its own hydroquinone is pretty aggressive, and metol is slow. Phenidone is not much better, but the discussion is MQ Thankfully we do have a range of chemicals that let us choose what happens, and how fast it happens. If we only had one developing agent, think of all the empty space on APUG...

 

[Arvee]

Glad you posted the graph. The one in Mason is very small and I believe gives a simple w/w ratio.

While we have you on the line, Gerald, I recall crediting you/reading in a post you made some similar information about optimal sodium sulfite content in M-Q developers - a value of 70 g/l. I believe you indicated deviation from this value in either direction would compromise the effectiveness of the developer. I could not revive the post. True, or has my memory gone to hell?!

 

[Gerald C Koch]

While we have you on the line, Gerald, I recall crediting you/reading in a post you made some similar information about optimal sodium sulfite content in M-Q developers - a value of 70 g/l. I believe you indicated deviation from this value in either direction would compromise the effectiveness of the developer. I could not revive the post. True, or has my memory gone to hell?!

The maximum rate of silver halide solvency in a high sulfite low pH developer is somewhere from 70 to 80 g/l of sodium sulfite. The more deviation from this range the less silver halide is dissolved. The effect is not restricted to just MQ developers. So you will see modern developer like Xtol at 75 g/l which produces finer grain.

 

[Ian Grant]

While we have you on the line, Gerald, I recall crediting you/reading in a post you made some similar information about optimal sodium sulfite content in M-Q developers - a value of 70 g/l. I believe you indicated deviation from this value in either direction would compromise the effectiveness of the developer. I could not revive the post. True, or has my memory gone to hell?!

Well the original 1927 Eastman Kodak Research Fine Grain Developer uses 62.5 g/litre Sulphite in the working solution, the Borax MQ developers like D76 are derived from a Wellington and Ward fine grain MQ Borax developer but via a few steps that also produced the early versions of DK50 and DK60 (with Borax rather than Metaborate).

1927 Eastman Kodak Research Fine Grain Developer

Metol . . . . . . . . . . . . . . . . . . 2 g
Sodium Sulphite (anhyd). . . . . . 100 g
Borax . . . . . . . . . . . . . . . . . . 2 g
Water to . . . . . . . . . . . . . . . . 1.6 litres

Ian

 

[David Lyga]

Metol and hydroquinone are a super-additive combination. Therefor the rate of development is enhanced. The is important for a low pH MQ developer like D-76 to avoid long development times. There is an optimum ratio for the two developing agents. For an MQ developer this is approximately 1 part metol to 6 parts hydroquinone. This is discussed in Mason* which contains a 'U' shaped graph of development time vs the MQ ratio. The low point occurs at 1:6 w/w.

* While not as up to date as Haist's magnum opus LFA Mason Photographic Processing Chemistry is still a very useful book. It should be on the library shelf of anyone interested in photographic chemistry.

I fully concur here, although, to me at least, 'synergism' becomes a more meaningful description than the technically more correct 'super-additive' parlance. I guess what I was seeking with this post is permission to call HQ not a 'developer' but, instead, a facilitator of metol. That, to me at least, seems more appropriate a title for this chemical.

The darkroom Cookbook covers super-additivity. The relevant text is at https://books.google.com/books?id=Ba_OCwAAQBAJ&pg=PA22&lpg=PA22&dq=hydroquinone+superadditivity&source=bl&ots=wOaJWcilP9&sig=U6of-KWA7CseoOhBMH_VlcwZbBI&hl=en&sa=X&ved=0ahUKEwjBzJei5eDRAhUI5GMKHSmDBhYQ6AEIMDAE#v=onepage&q=hydroquinone superadditivity&f=false (Google, if the link survives).

On its own hydroquinone is pretty aggressive, and metol is slow. Phenidone is not much better, but the discussion is MQ Thankfully we do have a range of chemicals that let us choose what happens, and how fast it happens. If we only had one developing agent, think of all the empty space on APUG...

Grahamp, I believe, is incorrect here: over and over the literature states that it is metol which is fast acting (though yielding lower contrast) and it is hydroquinone which is slower to act (albeit, yields higher contrast). - David Lyga

 

[Ian Grant]

There's a second Metol only variant of D76, DK76b published by Kodak research at the same time as DK76 both use Metaborate.

Eastman Kodak Research- DK76b

Metol . . . . . . . . . . . . . . . . . . 2 g
Sodium Sulphite (anhyd). . . . . . 100 g
Sodium Metaborate (Kodalk) . . . 2 g
Water to . . . . . . . . . . . . . . . . 1 litre


Eastman Kodak Research- DK76

Metol . . . . . . . . . . . . . . . . . . 2 g
Sodium Sulphite (anhyd). . . . . . 100 g
Hydroquinone . . . . . . . . . . . . . 5 g
Sodium Metaborate (Kodalk) . . . 2 g
Water to . . . . . . . . . . . . . . . . 1 litre


Ian

 

[grahamp]

David - Depends a lot on the conditions, mainly alkalinity. In the developers I use, metol on its own in moderately alkaline conditions takes its time producing density, while hydroquinone in strong alkali is quick and contrasty. But fast and slow are sloppy terms (and yes, I used them!). By and large, I would not choose a pure hydroquinone developer for general purpose photography. I might use either metol or M-Q (P-Q).

I am far from an expert on photochemistry (I'll leave that to Gerald, Ian, and several others).

 

[Rudeofus]

I fully concur here, although, to me at least, 'synergism' becomes a more meaningful description than the technically more correct 'super-additive' parlance. I guess what I was seeking with this post is permission to call HQ not a 'developer' but, instead, a facilitator of metol. That, to me at least, seems more appropriate a title for this chemical.

In order for a compound to be called 'photographic developer', it needs to satisfy two conditions:

1. reduction: reduce silver ion to metallic silver
   
2. discrimination: preferentially reduce silver ion in silver halide crystal which has already a small cluster of silver atoms stuck to it

Hydroquinone clearly satisfies both, so it's a photographic developer, period.

Now you could argue "but it doesn't act as one in D-76, it never reduces silver ion directly", to which I say "how do you know it doesn't, at least in the final stage of development?".

Let me state here, that there was lots and lots of research going on about this, not everything in this whole process is fully understood, and even less is published. The interaction between Metol and HQ is very complex, much more than the simple "Ag+ + Metol ---> Ag + Quinonedimine, Quinonedimine + HQ ---> Metol + Q, Q + SO32- ---> HQMS" structure we frequently see in literature.

 

[David Lyga]

Thank you Rudenfus for the clarification. It is amazing to me that STILL, in 2017, the actual photographic reduction is not fully known!!! Yes, HQ is, decidedly, a developer. But it 'superadds' immensely well with metol to make the combination an even greater developer by enhancing it's strength and also by rejuvenating by it. - David Lyga

 

[David Lyga]

David - Depends a lot on the conditions, mainly alkalinity. In the developers I use, metol on its own in moderately alkaline conditions takes its time producing density, while hydroquinone in strong alkali is quick and contrasty. But fast and slow are sloppy terms (and yes, I used them!). By and large, I would not choose a pure hydroquinone developer for general purpose photography. I might use either metol or M-Q (P-Q).

I am far from an expert on photochemistry (I'll leave that to Gerald, Ian, and several others).

OK, I defer... with sodium hydroxide (ouch!) HQ does, indeed, 'take off'. - David Lyga

 

[Rudeofus]

Thank you Rudenfus for the clarification. It is amazing to me that STILL, in 2017, the actual photographic reduction is not fully known!!!

A lot of stuff is known, and the reactions taking place are well understood on a quantum mechanical level. What is, AFAIK, not understood, is why one development agent gives different granularity from another, or why discrimination between developable and undevelopable silver halide differs from development agent to development agent, sometimes in quite peculiar ways.

Yes, HQ is, decidedly, a developer. But it 'superadds' immensely well with metol to make the combination an even greater developer by enhancing it's strength and also by rejuvenating by it.

You tend to underestimate HQ's role in development. The way it restores oxidized Metol appears to be different from other secondary developers like Ascorbic Acid, Catechol, Pyrogallol or HQMS, so you get different photographic results from MQ, MC, M-Catechol, M-Pyro and M-HQMS developers. Also note, that not all oxidized Metol gets restored during development, some reacts with Sulfite ion to form Metol Sulfonate, which both inhibits development by other Metol molecules, and is a weak developer by itself.

As I mentioned before, the action of superadditive developers on silver halide crystals is pretty complex, and the above only scratches the surface of the whole story: think of pH changes from development reactions and their effect on developer reduction potential, adsorption of fresh and oxidized developer molecules to silver and silver halide, development inhibition by released halide ions. Different diffusion of fresh, oxidized and scavenged development agents gives different local exhaustion effects, and some oxidized developers harden gelatin. Half way developed silver halide crystals need less reduction potential and might see development by secondary agent, which wouldn't develop small development centers under same conditions. Add to this different sized silver halide crystals, a range of different sensitizer molecules firmly stuck to each crystal, and multiple layers of this coated on the base.

The deeper you dig, the messier it gets. Calling the synergy of two development agents 'superadditive' covers a big area of wildly different situations, but it's an established term, it's been used by folks who spend decades researching and knew a lot more about this than the both of us, so we might as well stick to it.

 

[Alan Johnson]

IMO superadditivity is pretty well explained on p377-8 of Mees & James 3rd Ed. There are two theories, the charge barrier theory which applies more at high pH~10 and the better known regeneration theory applying more at low ph, ~8.7, which would be the case discussed here.You have to know your aminophenols from your electrode potentials.

 

[David Lyga]

Rudeofus is a font of information: a true asset. And, thank you as well, Alan. - David Lyga