MCM 100 film developer

Alan Johnson · Jul 16, 2016

Jay DeFehr has a PPD developer adapted for the newly popular ascorbate, see post 30 for his explanation of how it works:
http://www.largeformatphotography.i...?71010-Halcyon-superfine-grain-film-developer

Gerald C Koch · Jul 16, 2016

Alan Johnson said:
Jay DeFehr has a PPD developer adapted for the newly popular ascorbate, see post 30 for his explanation of how it works:
http://www.largeformatphotography.i...?71010-Halcyon-superfine-grain-film-developer

The problem with PPD, other than its toxicity, is that it is just a very poor developing agent yielding poor film speed, poor tonal separation, poor contrast, and long development times. In order to get anything approaching satisfactory results it has to be used in combination with one or more different developing agents. If you google the name most hits as to its photographic use describe it as an obsolete developer replaced by more modern agents.

darkroommike · Jul 17, 2016

Start a new thread and keep us posted!

Gerald C Koch · Jul 17, 2016

michael_r said:
A simple experiment I've wanted to do, is to simply add 1 or 2g of sodium ascorbate to D-23 and see what happens compared with plain D-23.

Hi Michael,

If your thought is to investigate SA then a deceptively simple experiment is actually more involved.

First, you need to make sure that the pH, and other things of the developers are constant throughout the test.

Second, just adding more developing agent will cause shorter development times simply because there is more developing agent. Remember that Mason kept the total molar concentration of developing agents constant and then varied the molar ratio of the two. I think such a series of experiments would yield some interesting results. Again one has to be careful. The total amount needs to remain constant.

A second series of experiments could be with two developing agents that do not form a SA pair. A good set would be catechol and sodium ascorbate. Then compare the two series.

Anyway have fun.

Jerry

Rudeofus · Jul 18, 2016

michael_r said:
Unfortunately it seems impossible to produce good p-aminophenol. I've tried ordering both the HCL and free base (should have a more stable shelf life), and in both cases I received bottles of dark purple-brown crystals.

As the example of Rodinal shows, brown discoloration doesn't seem to hurt overall activity of p-Aminophenol. Either way, the bottle of p-Aminophenol I received from Suvatlar over a year ago is still pure and white, and it has been open for a while now, and stored at room temperature which can get quite high here (>30°C). Given all that, I have no idea how a chem supplier can have the guts to actually sell and ship purple-brown p-Aminophenol, they should be ashamed of themselves.

Alan Johnson · Jul 18, 2016

michael_r said:
Another experiment I've wanted to do along the same lines, is with p-aminophenol and ascorbate at a weakly alkaline pH (ie atypical for p-aminophenol). My dream there was to make a general purpose fine grain developer with zero fog. Unfortunately it seems impossible to procure good p-aminophenol. I've tried ordering both the HCL and free base (should have a more stable shelf life), and in both cases I received bottles of dark purple-brown crystals.

I did try something like this,starts at post 28 in the link,but at pH 10+ the grain was not very fine. It's simple to make p-aminophenol from paracetamol/Tylenol.
(there was a url link here which no longer exists)
It may be that sulfite or PPD or thiocyanate is needed to redeposit silver from the developer to give fine grain.

Gerald C Koch · Jul 18, 2016

P-aminophenol does not have to be used at high pH. Kodak at one time sold it as Kodelon to be substituted for metol and not cause allergic reactions. So it will work perfectly fine in developers like D-23 and D-76.

You can take advantage of the fact that PAP free base is insoluble in water or mild alkalis. It you have the free base first dissolve it in dilute HCl and then add a solution of sodium carbonate containig a bit of sodium sulfite. The PAP will precipitate and can be filtered off leaving most of the dark color behind. A bit of decolorizing charcoal helps here too. If you have the HCl salt then just skip the first step. This is how I discovered that Rodinal is a pale lavender color when freshly made.

Gerald C Koch · Jul 18, 2016

I've never seen any mention that PAP needs a higher pH than metol. What is usually mentioned is that the developing agent produces very little fog and is therefore used in tropical developers. It should be easy to check just put some in a sodium sulfite solution and see what it does. Perhaps with a pinch of borax.

Alan Johnson · Jul 18, 2016

Jerry there is also a diagram Fig 16.11 on p361 of Mees & James 3rd ed that shows the density obtained by developing film in various developers vs pH, for a fixed time of development. It definitely appears that metol is more active than p-aminophenol and much more active than PPD at low pH.
This suggests that metol is the preferred agent if it is hoped to obtain fine grain by lowering the pH.

Gerald C Koch · Jul 18, 2016

Metol with some ascorbate sound a bit similar to Ryuji's DS-12.

Rudeofus · Jul 19, 2016

Alan Johnson said:
Jerry there is also a diagram Fig 16.11 on p361 of Mees & James 3rd ed that shows the density obtained by developing film in various developers vs pH, for a fixed time of development. It definitely appears that metol is more active than p-aminophenol and much more active than PPD at low pH.

There are (at least) three parts to activity of a development agents, they have different causes and effects and are not always present:

Reduction potential - typically pH dependent. pH vs. reduction potential curves are available in literature
Charge barrier - typically dependent on overall electrical charge of active developer molecule/ion. High negative charge usually translates into low apparent activity.
Self restraining effects: some developer molecules bind to silver or silver halide even in their oxidized state, which bloks access of fresh developer molecules to image centers.

Well known development agents which suffer from self restraining effects are Phenidone and PPD, and both can be combined with other compounds to form very active developers. Note, that Metol and p-Aminophenol would also suffer from this effect, however, they are effectively scavenged by Sulfite and can therefore be used alone.

Rudeofus · Jul 19, 2016

michael_r said:
Rudi - Is the stuff you got from Suvatlar the free base or HCL salt? It isn't clear from the price list as there are no CAS numbers. I guess I could just send them an email.

The bottle states 'p-Aminophenol', with CAS number 591-27-5 and molar weight 109.13, all of which would suggest free base.

If I try to dissolve it a DI water, it dissolves poorly and pH is near neutral - which is weird, since I would have expected an alkaline pH. Just sent a mail to Suvatlar for clarification.

michael_r said:
I had always assumed rodinal goes brown because of a small amount of oxidation producing strong coloration, but I wonder if I can use the crystals I got even though the are ALL dark brown/purple.

If crystals catch some water from ambient humidity, they could oxidize just as well as they do in Rodinal. Since it would be very difficult to check whether these crystals are dark brown throughout or just on their surface, I suggest you dissolve some in water - about the same quantity that you would have in Rodinal 1:25 working solution. If your mix is not substantially darker than Rodinal 1:25 working solution mixed from dark brown concentrate, then I would think that your batch is fine.

Gerald C Koch · Jul 19, 2016

michael_r said:
In the table in Haist (from a kinetics study by M. H. Dickerson) p-aminophenol needed a pH of 9.35 to develop at the same rate as metol at pH 7.25. Granted this is essentially data about development speed, which isn't that important to me since I don't mind long development times.

A pH of 9.3 is considered normal for many developers. I saw the term high pH and immediately thought of developers in the range pH 10 to 11. The actual figure clears things up. But considering the activity of the chemical itself the data was still surprising. I have seen a moist, freshly prepared sample of the free base begin to turn brown around the edges in a few minutes. Thanks.

How long a sample of PAP takes to turn color also seems to be related its purity. Less pure samples will darken more quickly.

Rudeofus · Jul 20, 2016

Rudeofus said:
The bottle states 'p-Aminophenol', with CAS number 591-27-5 and molar weight 109.13, all of which would suggest free base.

If I try to dissolve it a DI water, it dissolves poorly and pH is near neutral - which is weird, since I would have expected an alkaline pH. Just sent a mail to Suvatlar for clarification.

Just got confirmation from Suvatlar, that p-Aminophenol free base is sold in his bottles. The CAS number on my bottle is wrong BTW, it should read 123-30-8, also conformed by Suvatlar.

Rudeofus · Jul 21, 2016

michael_r said:
Incidentally, what is the correct molecular weight for metol? Depending on where I look I get different results for the same cas #.

Depends on what you see as one molecule. If you see Metol as di-(p-Methylaminophenol) Sulfate, then you have a mol weight of 2*123.15 + 98 = 344.3 g/mol. If you see Metol as p-Methylaminophenol Hemisulfate, you have a mol weight of 172.2 g/mol. If you just look at the free base p-Methylaminophenol, your mol weight will be 123.15 g/mol. Did you see numbers different from these three?

Rudeofus · Jul 21, 2016

The term 'mol' by itself is meaningless unless you state which molecule you refer to. The generic definition means 6.022140857×1023 molecules. But look at e.g. Sodium Metaborate Tetrahydrate: this compound can be written as NaBO2 * 2 H2O, or as Na2B2O4 * 4 H2O. Two mols of NaBO2 * 2 H2O in solution will give you the exact same liquid as one mol of Na2B2O4 * 4 H2O.

You have the same thing with Metol: two mols of p-Methylaminophenol Hemisulfate (mol weight 172) give you the exact same number of atoms in the exact same configuration as one mol of di-(p-Methylaminophenol) Sulfate (mol weight 344). You can argue for both: there is no such thing as a Hemisulfate molecule ---> 344 is correct, or: you use Metol for its p-Methylaminophenol component, and one mol of p-Methylaminophenol Hemisulfate will supply one mol of p-Methylaminophenol to your solution ---> 172 is correct.

As long as you stick to the same definition of 'Metol molecule', you can use either number.

Gerald C Koch · Jul 21, 2016

344.38 g/mole is the amount given in the MSDS. It really doesn't matter what basis you make your calculations on, either as the hemisulfate or the sulfate. However you must be consistent in your calculations. That is, use one or the other value all the time. It's the same as going to the market and asking the price of eggs. One clerk will say $1.19 for half a dozen while another will say $2.38 a dozen.

But for the average photographer you will not has have to consider moles. If your making D-76 the amount per liter is 2 g. You really don't need to know how many moles this represents.

Gerald C Koch · Jul 21, 2016

michael_r said:
I'm confused. Perhaps an example:

I want to do a mol/mol substitution of 2g metol for xg p-aminophenol. Either:

2/x = 344/109 or
2/x = 172/109

Which is correct?

Michael write out a balanced equation for converting PAP to metol. Everything should be clear then.

Alan Johnson · Jul 21, 2016

Look up p-aminophenol on wikipedia, it only has one carbon ring.
The figure 344 for metol is quoted for two carbon rings,but just to confuse the uninitiated, not by Sigma Aldrich:
http://www.sigmaaldrich.com/catalog/product/sial/69750?lang=en&region=GB
For an equivalent to 1 carbon ring of p-aminophenol you only need 1 carbon ring of metol, 172.2 g

Gerald C Koch · Jul 22, 2016

The molecular weights represent TWO different things. A single molecule of PAP with 1/2 a molecule of sulfuric acid OR two molecules of PAP and one molecule of sulfuric acid. Obviously you cannot have half a molecule of sulfuric acid hence the fiction. As long as one is consistent with which model one uses there will be no problems.

MCM 100 film developer

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