An interesting aspect of acutance developers

Gerald Koch · Mar 24, 2006

Some food for thought. There are two ways of compounding an acutance developer. The most common method is to limit the amount of developing agent. However, there is a second method and that is to limit the amount of preservative. This is usually sulfite but could also be some other chemical. Kodak used this second method in their HDD High Definition Developer. The amount to sodium sulfite was half that of the Metol. This ratio ensured the controlled decomposition of the developing agent.

Jordan · Mar 24, 2006

Gerald, what kind of image does a solution of metol in base (no sulfite) make?

Gerald Koch · Mar 24, 2006

The HDD developer contains some sulfite. The proportions of developing agent to sulfite are somewhat the reverse of the Beutler formula or FX-1. Some sample images are at Dead Link Removed

sanking · Mar 24, 2006

Gerald,

From my look at the literature it appears that the majority of high acutance developers do both, i.e. they limit the amount of developer, *and* use a very small amount of preservative.

There are likely other methods to achieve high acutance about which scientists like Ryuji and PE might want to comment, but the majority of high acutance formulas that I have seen contain very small amount of reducer per liter of working solution, typically 1.0g or less, and a very small amount of sulfite, 5.0g or less (and sometimes, as with PMK and Pyrocat-HD, much, much less).

The use of a secondary reducer, say Pyrogallol + metol in PMK or Pyrocatechin + phenidone in Pyrocat-HD results in a combination that has greater synergism than would be seen with Pyrogallol or Pyrocatechin alone, and alters somewhat the relationship between amount of reducer and acutance. A third reducer complicates the situation even more and none of the formulas with three reducers that I have tested, Rollo Pyro for example, could be considered true acutance developers, though they may give apparent sharpness that is perfectly acceptable for the task.

Also, both degree of enlargement and type of agitation plays a very major role in determing how much acutance is needed and can be obtained. The most difficult design parameter is the combination of rotary or other means of continuous agitaiton and very high acutance.

Sandy

Gerald Koch said:
Some food for thought. There are two ways of compounding an acutance developer. The most common method is to limit the amount of developing agent. However, there is a second method and that is to limit the amount of preservative. This is usually sulfite but could also be some other chemical. Kodak used this second method in their HDD High Definition Developer. The amount to sodium sulfite was half that of the Metol. This ratio ensured the controlled decomposition of the developing agent.

Alan Johnson · Mar 25, 2006

Metol/sulfite was looked at by G.W.Crawley BJP 6 Jan 1961.To prevent regeneration of the metol sufficient to improve definition,sodium sulfite (anhyd) must be below 6g/L.Below 5g/L film speed drops so that at 2-3 g/L it is normal and the inhibition of developer regeneration sharpens up the picture markedly.Below 4 g/L keeping properties of the solution are affected.At 1 g/L there is a marked sharpness increase but the developer must be used immediately.Metol will work very slowly in absence of sulfite altogether.
The non-availability of fresh developer has some tendency to prevent image spread due to the infection of adjacent crystals,the effect can be promoted by reducing the preservative content of the formula to inhibit regeneration of the developing agency.(My summary of part of the article)

gainer · Mar 25, 2006

Now we can play with the Metol base in TEA or glycol so there is little worry about oxidation of the stock. Due to my experiments, I have so many bottles of Metol base in glycol that I don't know what to do with it all. It is in the equivalent of 10% solution of Metol in propylene glycol, but without the sulfuric acid on its tail, and you all know that one liter of such a solution is a lot of Metol.

I have a feeling that a little Metol and a little TEA will blacken a lot of film. It may require some alkali metal to form a water soluble salt. I shall retire to the dungeon and find out.

Alan Johnson · Mar 25, 2006

G.W.Crawley suggested this formula for immediate use: Sodium sulfite anhyd 1g ,metol 0.5g ,sodium carbonate anhyd 3g , water to 1L. Develop 15-20 min or longer.The films GWC used are gone except Adox KB14 and may affect the result.

gainer · Mar 25, 2006

I did my work in the dungeon and found that the metol base along with the metaborate "B" solution from PMK gives good results without sulfite, though a tiny bit of sulfite will speed it up. I'm going to try my luck at posting a picture in the Technical Gallery.

gainer · Mar 25, 2006

It's in the Experimental Gallery.

dancqu · Aug 28, 2007

I brought forward this thread because of the
interest in the subject stirred by the discussion
surrounding the very dilute D-23 I tested.

Alan Johnson's posts describe further some of Crawley's
work. Very interesting is Crawley's observation that
regeneration is not desirable. Dan

Photo Engineer · Aug 28, 2007

There are several other routes to high acutance. Kodak had developed several of these to commercial levels, but some of the best still rest in notebooks at the Research stage.

None of them use any of the above methods.

PE

Alan Johnson · Aug 29, 2007

G.W.Crawley (1961) seems to have considered that apparent sharpness is comprised of both 'knife-edge' acutance and adjacency effects.(The two together are also often called acutance)
In 1961 he reported that the small addition of potassium iodide to FX-1 promoted adjacency effects with some films of that time.When I wrote to him recently he replied 'There is indeed no point in adding potassium iodide to FX-1 with modern films'.This suggests to me that modern films don't give the same adjacency effects and if a developer is of the type that gives adjacency effects it will do better with older films.I have obtained good adjacency effects in stand development tests with Adox CHS 25 &100,Plus-X and Tri-X, depending on format.
If a developer is of the type that does not produce much adjacency effect,and its sharpness is due to knife-edge acutance, it should work well with modern films as well,IMO. G.W.Crawley (1961) appears to refer to 'knife-edge' acutance when he wrote 'when the concentration of developing agents is lowered....the non-availability of considerable supplies of fresh developer has some tendency,more marked with slightly sharper crystalled emulsions,to prevent the image spread due to the infection of adjacent crystals.This effect can be promoted by reducing the preservative content of the formula to inhibit regeneration of the developing agency.'

Photo Engineer · Aug 29, 2007

Edge effects by 'restraint' can only be gained by the imagewise release of either bromide or iodide or by exhaustion of developer or pH. If you add iodide to a developer, it is not present imagewise, but rather is uniformly distributed. If a 'edge' is gained by this method it would be virtually miniscule compared to what the emulsion can release in terms of bromide or iodide.

Dilute developers or high pH developers with low buffer capacity can do much the same.

Silver halide solvents can do this by releasing iodide or bromide imagewise, but they are less effective as their action is more uniform throughout the image similar to adding iodide to a developer.

All of this is true for old and new films, as the high speed films all contained iodide to some extent.

PE

dancqu · Aug 29, 2007

Alan Johnson said:
Metol/sulfite was looked at by G.W.Crawley BJP 6 Jan 1961.

To prevent regeneration of the metol sufficient to improve
definition, sodium sulfite (anhyd) must be below 6g/L. ...at
2-3 g/L...the inhibition of developer regeneration sharpens
up the picture markedly. ...At 1 g/L there is a marked
sharpness increase but the developer must be
used immediately.

Well that above was news to me! I've always thought of the
low sulfite issue as being one of reducing the sulfite's solvency.
Very one shot I'd say lowering the sulfite level below that needed
to regenerate. Crawley's 0.5, 1.0, grams metol, sulfite plus some
carbonate formula you've mentioned in a post this thread may
not be practical.

I fully processed a roll of 120 with a formula 0.6, 1.8, 1.8 metol,
sulfite, carbonate brew and poured from the tank yellow developer.
Then again I've processed paper in a non-sulfited developer
and had clean paper from a black developer. SO? Dan

Alan Johnson · Aug 29, 2007

The debatable effect of potassium iodide in promoting adjacency effects is a bit of a red herring, since it is known that the Beutler developer produces these effects without any, see 'Controls in Black and White Photography' by R. Henry,p240. The idea that developers producing adjacency effects should work better with old films worked with the films I tested.

dancqu · Aug 30, 2007

dancqu said:
Well that above was news to me! I've always thought of the
low sulfite issue as being one of reducing the sulfite's solvency.
Very one shot I'd say lowering the sulfite level below that needed
to regenerate. Crawley's 0.5, 1.0, grams metol, sulfite plus some
carbonate formula you've mentioned in a post this thread may
not be practical.

I fully processed a roll of 120 with a formula 0.6, 1.8, 1.8 metol,
sulfite, carbonate brew and poured from the tank yellow developer.
Then again I've processed paper in a non-sulfited developer
and had clean paper from a black developer. SO? Dan

I should have mentioned that a half liter of that 0.6 formula
was used; so 0.3, 0.9, and 0.9 grams were present in the
tank. Actually that is a small portion of an Ansco 120 or
Beer's A. formula. The ratios are the same as those of
Beutler's save for the reduced sulfite; 1:3 vs 1:5.

BTW our differences over the D-23 to FX-1 is anhydrous
vs mon-hydrate; 40 vs 48 grams. Dan

Alan Johnson · Aug 31, 2007

BTW, there is a problem for amateurs in assessing developers for acutance,IMO.This is of interest esp. for new ones that are devised.
I don't think it is possible for the amateur to measure the knife-edge acutance of a film with different developers.It was formerly done with a microdensitometer.Some modern films seem to mainly depend on knife-edge acutance for apparent sharpness.
It may be possible,I believe, to differentiate the adjacency effects of different developers by photographing a gray card on a black card ,stand developing, and making a 10x enlargement of the edge using one of the aforementioned 'old' films.The effect shows as a light line on the gray edge on the print.

Photo Engineer · Aug 31, 2007

You can use a positive and negative resolution chart set sold by Edmund scientific. Using both gives a feel for acutance.

These charts are metal depositied on glass and are contact printed onto the film.

The measurement of this as done at EK involves a pair of X-ray and light exposures to metal slits of varying sizes. This allows the researcher to separate out turbidity and other optical effects from true sharpness as the difference between the x-ray and visible light exposure is the measure of turbidity.

PE

dancqu · Oct 8, 2007

dancqu said:
Well that above was news to me! I've always thought of the
low sulfite issue as being one of reducing the sulfite's solvency.
Very one shot I'd say lowering the sulfite level below that needed
to regenerate. Crawley's 0.5, 1.0, grams metol, sulfite plus some
carbonate formula you've mentioned in a post this thread may
not be practical.

I fully processed a roll of 120 with a formula 0.6, 1.8, 1.8 metol,
sulfite, carbonate brew and poured from the tank yellow developer.
Then again I've processed paper in a non-sulfited developer
and had clean paper from a black developer. SO? Dan

Once again I've brought forward this thread. My excuse;
a question from Mr. Gainer. The issue is metol's regeneration
by sulfite. Alan Johnson's posts this thread are germane. Dan

gainer · Oct 8, 2007

The article that I read from Mees & James and used as the basis for my experiments with Metol and ascorbic acid had graphs that appeared to show that sulfite and ascorbate were about equivalent in their effects on activity of a Metol developer at pH = 8.7 It was explained in the text that although the effects appeared equal, the mechanisms were different. Sulfite IIRC scavenged the metol products of oxidation that tended to inhibit development, while ascorbate restored the oxidized Metol to its unoxidized form. I think that there are differences that one would find in practical use that influence the effect of ratio of area of film to volume of developer, as well as effects of different amounts of agitation.

At the low pH of 8.7, it's fairly certain that superadditivity in the usual sense is not acting. Ascorbic acid is an antioxidant even in acidic solutions. Though it wouldn't turn exposed film black, it appears capable of reducing oxidized developer. I don't know enough chemistry to know what I'm talking about, but I understand a little of what others are saying. Knowing that there is evidence that the mechanisms by which sulfite and ascorbate ions effect the action of developers even in cases where the apparent results are the same gives me some kind of license to investigate and to try to get some others who have a little time on their hands to do likewise.

The article in the "Theory ----" article compared solutions of sodium sulfite and ascorbic acid, each containing Metol and adjusted to pH=8.7. The same mole percent of each produce the same resulting graph, which showed increased activity with increasing percent until levelling off at 0.05 M. That is, 6.3 g/l of sodium sulfite was equivalent to 8.8 g/l of ascorbic acid.

This article was not even a full page, although the full paper was listed in the references.

I've run out of steam-- or is it hot air?

Photo Engineer · Oct 8, 2007

I think that the bottom line to me, after years of compounding developers, is that AA is chancy to use (see the Xtol problems if it is not packed properly or the problems with spontaneous 'death' of Xtol).

Sulfite however is repeatable.

This is why I tend to avoid AA developers unless they are mixed and used fresh.

Sulfite does indeed add chemically to oxidized Metol and HQ to produce the sulfonate of the developers. AFAIK, only the HQ monosulfonate is a developer of itself, and it is weak. The ration is about 1 HQ = 5 HQMS. That is a very very rough guesstimate.

HQMS has many good properties. My reading of Mees and James show little or no good effects from Metol reaction products with sulfite. I will re-read the topic again to make sure I have not missed anything.

The idea of a HA developer (high acutance) is to form fine grained silver particles with good edge effects. There is a lot that can be done here, but among other things, edge effects are NOT gained by adding iodide or bromide to the developer. In general, that represses edge effects. Edge effects are enhanced by low buffer capacity or low developer concentration so that exhaustion can accentuate edge effects.

Grain minimization is another matter and is usually accomplised by reductions in speed.

PE

gainer · Oct 9, 2007

When AA is used as if it were HQ, as part of a synergistic, I suspect the loss of half the AA by whatever mechanism might be a catastrophe. However, even when synergism is involved, there appears to be a levelling off of the effect as AA is increased. I did and presented some such experiments a few years ago. I was convinced I had shown that increasing AA beyond about a 50:1 ratio to Phenidone had little or no effect on the developer activity, but might at least serve as a cushion against catastrophic failure and allow more film to be developed per unit volume of developer.

The use of AA as a simple antioxidant, if that is what is happening at around pH=9, would seem to extend its usefulness to nearly complete exhaustion of its antioxidant powers. It might have a very different function than it does in XTOL.

I'd better quit before I get too far behind.

Alan Johnson · Oct 9, 2007

Crawley's article BJP Jan 6 1961 does say 'To prevent regeneration of the developing agency ....the concentration of sulfite must be kept below 6g/L'
However, looking at the thread on superadditivity,esp posts 47 & 54:
(there was a url link here which no longer exists)
There it is noted that the oxidation of metol (development) is speeded up because sulfite removes one of the reaction products.Specifically, unlike Crawley, it does not say the metol is regenerated.
It's not clear if Crawley's writing could have been worded better.

gainer · Oct 9, 2007

What is observed as superadditivity may be the result of two developing agents acting together more actively than the sum of the individual activities would predict. It is usually the case, perhaps because most of us do not make developer solutions without sulfite, that sulfite is required for the synergiasm to operate. The fact that the curves obtained by James and presented also in "The Theoty of the Photographic Process" show ascorbic acid acting, it would seem, synergistically with Metol without sulfite might seem an anomaly. However, the same effect is seen when an equal molecular weight of sulfite is substituted for the ascorbic acid, an identical effect is seen. This effect was not produced by the substitution of an equal molecular weight of hydroquinone. Do these observations mean that sulfite is superadditive with Metol while hydroquinone is not?

The activity of the Metol was practically doubled by 0.025 M of either sulfite or ascorbic acid, and increased very little with the addition of more of either. James determined that the sulfite formed the Metol sulfonate, which is not an active developing agent, thereby indicating that the oxidation product of Metol is a development retarder. The ascorbic acid OTH restored the Metol. We might predict that had the experiment been carried on so that any given solution became exhausted, the ascorbic acid solution would have considerably outlived the sulfite solution. Remember, only about 6 grams per liter of sulfite were used. Even had more been used, the Metol would sooner or later been converted to the sulfonate, which is very much weaker than Metol, and the rate of development would gradually decrease as the Metol was used up. It would seem that the ascorbic acid solution should retain the same activity except for the effects of bromide buildup until the bitter end. The bitter end can be delayed considerably by increasing the concentration of ascorbic acid without causing the deleterious effects of high sulfite concentration. True, the greater the concentration, the shorter the time constant for regeneration, which may have undesirable effects on edge effects etc. I have not seen these yet. I do see considerable evidence of image-proportional tanning in the Metol-ascorbic acid developer. The lenticular effects of this tanning are said to produce some degree of apparent sharpening.

I'm not preaching, but trying to stir up some interest in more testing than my 80 year old body will tolerate.

Photo Engineer · Oct 9, 2007

Patrick;

Any chemical reaction in which another ingredient removes one of the reaction products, by whatever means, is speeded up.

So, A + B = C and if D is present and reacts with C, then the reaction A + B becomes faster by some constant amount depending on the removal rate of C. This is a basic fundamental fact of chemical equllibria.

If D regenerates A or B by reaction with C, then the reaction is sped up even more by supplying one of the starting materials.

This is changed if D removes A or B.

If D = Sulfite, A = HQ and B = Oxygen in water, then C = HQ monosulfonate. This leads to the well known drop in activity of HQ developers as oxygen is used up and HQ monosulfonate is used, and also is the reason for adding a pinch of sulfite to water before adding HQ or Metol to use up the oxygen.

You can substitute silver halide or metol into this equation as well or, well, just about any ingredient you want to and come up with K (rate constant) by measuring the rate at which things form or vanish from solution.

PE

An interesting aspect of acutance developers

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