Caffenol's ascorbic acid activity

[elerion]

Even though I search for quite long, I haven't found an explanation for this yet.

- Ascorbic acid is NOT superadditive with chlorogenic/caffeic acid; both are in the same group as HQ (from SA point of view). So, ascorbic acid is NOT restoring the other developer agent. They are both working in parallel.
- Ascorbic acid-only developers require very high pH and are slow. SALS13, by ErikP (http://ascorbate-developers.blogspot.com/2011/03/sodium-ascorbate-sals-12.html) works at pH 13, using NaOH, and even though, development time seems to be not particulary short (let grain and contrast issues aside).
- Caffenol receipes' pH seem to be in the range 10.2-10.8, which makes sense, as they use sodium carbonate as alkali.

If all this assumptions are correct, then, ascorbic acid should not be active at the pH used in most Caffenol receipes.
But, it does have an impact. Some people wrote that it maybe reduces fog. I don't know. Some others wrote that it increases contrast (as if adding HQ to metol or phenidone). But, AFAIK, this should not be the case.

Can anyone share some thoughts about this?

 

[removed account4]

hi
sorry in advance to be not much help but ...
you might have better luck researchng your caffneol
over on the various coffee developer blogs. these days
there don't seem to be many people here from the coffee blogosphere

i can tell you that people figured out its not caffic acide but "other stuff" in coffee that
develop film and prints, no clue what it is nor do i worry too much about it

have fun with your studies !
john ( coffee drinker, coffee roaster and caffenol user )

 

[elerion]

jnanian thanks. I know there're not lots of people here that praise caffenol, but there're people who are interested in chemistry.
Honestly, I rarely use Caffenol. I really dislike the smell
But I like to know the technical stuff, not just get things working.

 

[Alan Johnson]

There has been some speculation that coffee might contain a substance X which is superadditive with caffeic acid, see eg post 7 here:
https://www.photrio.com/forum/threads/caffeic-acid-fill-of-beans.115988/
If X is superadditive with both ascorbic and caffeic ions , this would be consistent with the increase in activity of caffenol on addition of ascorbate.
cf phenidone superadditivity with catechol and ascorbate in a Pyrocat version with added ascorbate.
There has been very little published on ascorbate chemistry and nothing on its increasing activity of other secondary developers like hydroquinone.

 

[removed account4]

hi alan
i have the memory of a fish .. i had forgotten that
you experimented with pure caffic acid and got good results
as the link suggests it could be 1 of between 600 and 1000 things that
could be the X Factor ..

jnanian thanks. I know there're not lots of people here that praise caffenol, but there're people who are interested in chemistry.
Honestly, I rarely use Caffenol. I really dislike the smell
But I like to know the technical stuff, not just get things working.

totally understandable !
i don't even smell it anymore to be honest .. not sure if you know the old joke
Q: how do you know how long to process your film in caffenol?
A: until you can't stand the smell !

btw its the washing soda that makes it smell bad

have fun figuring out the answers to your questions
john

 

[NedL]

This article says over 1000 different compounds in coffee. When I first started roasting coffee, I read somewhere >300 volatile and >300 non-volatile compounds.

 

[removed account4]

This article says over 1000 different compounds in coffee. When I first started roasting coffee, I read somewhere >300 volatile and >300 non-volatile compounds.

LOL exactly !
id rather leave it a mystery with " compound X "

 

[elerion]

id rather leave it a mystery with " compound X "

Agree.
That X (or Xs, plural) must be present in tea too (green/back tea, not TEA, just in case...), and other vegetable sources, which some people have used to develop film (like potatoes or eucalyptus' bark).

 

[removed account4]

you mean like this guy
https://www.photrio.com/forum/threads/edible-film-developers.33501/

 

[Alan Johnson]

Some substances are known to be superadditive with ascorbate, hydroquinone and possibly other ingredients like caffeic acid and edible materials.
Such substances include phenidone and metol, which are, by one theory at least in part adsorbed on the grain surface and just pass electrons from ascorbate, hydroquinone etc.Notably, phenidone and metol are small molecules. So, if substance X is superadditive with caffeic acid in caffenol, sustance X is likely to be a small molecule.I am not saying this is true but it would fit the observed facts-look for small molecules in coffee.

 

[elerion]

Didn't know about that thread.
Nice talk!

Alan, interesting observation. I didn't know about the size of phenidone. It always seemed to me like a big molecule... bigger than HQ and most benzene ring like molecules.

 

[Alan Johnson]

Good chart giving approximate molecule sizes elerion. Perhaps X is a little bigger than one benzene ring.

 

[Rudeofus]

Some substances are known to be superadditive with ascorbate, hydroquinone and possibly other ingredients like caffeic acid and edible materials.

As I mentioned in this thread you referenced, superadditivity between coffee ingredients and Ascorbic Acid may not even be the driving force here. Certain wetting agents can strongly accelerate development by otherwise very slow developing agents like Ascorbic Acid, HQ and even HQMS, even if these wetting agents show no developer activity on their own.

 

[elerion]

As a side note, I recently read somewhere (in someone's web, not a book) that ascorbic and phenidone don't follow the Kendall-Pelz rule, but they do.
Ascorbic molecule has OH-(C=C)-OH on the top-right (on my attachment), which clearly places it in HQ group.
Phenidone can be converted to OH-(C=N)-NRR, if I'm not mistaken. There was a thread about Kendall-Pelz rule here.

Certain wetting agents can strongly accelerate development

Wetting agents are many times overlooked. Most people have heard the term only relating to the final wash of film (i.e photo flo).

 

[Rudeofus]

As a side note, I recently read somewhere (in someone's web, not a book) that ascorbic and phenidone don't follow the Kendall-Pelz rule, but they do.
Ascorbic molecule has OH-(C=C)-OH on the top-right (on my attachment), which clearly places it in HQ group.
Phenidone can be converted to OH-(C=N)-NRR, if I'm not mistaken. There was a thread about Kendall-Pelz rule here.

There is a good description of this in Grant Haist's "Modern Photographic Processing", highly recommended reading BTW, and quite a bit easier to read than T. H. James's "Theory of the Photographic Process".

Allow me to provide you here with a very brief summary:

Early in the 20th century researchers tried to establish rules for determining, whether a compound would work as photographic developer. There were the Lumiere- Andresen rules, which covered aromatic rings with two substituents of type -OH and -NH2 in ortho or para position, and possibly some extra substituents, and which also described how substituents would affect developer activity. This Lumiere-Andresen rule covers many developing agents still in use today, but it does e.g. not cover Hydroxylamine or most color developers.

This Lumiere-Andresen rule was then extended by Kendall, who included any carbon chains with alternating single and dual bonds, and which also included a wider range of substituents. This is the Kendall rule, which is frequently written as A-(C=C)n-A' with A from -OH, -NH2, -NHR1 and -NHR1R2.

As you can see, the Kendall rule in its original form would not classify Phenidone (which was found by Kendall anyway, that's why this whole issue is even mentioned so often) as a developer. The Kendall rule was therefore extended to include A-(C=C)n-A' and A-(C=N)n-A', and this extended form is called Kendall-Pelz rule. And yes, the Kendall-Pelz rule correctly classifies Phenidone as photographic developer.

Wetting agents are many times overlooked. Most people have heard the term only relating to the final wash of film (i.e photo flo).

Wetting agents as development accelerators were certainly not overlooked in scientific research. They were found to be inferior to typical primary development agents such as Metol and (substituted) Phenidone, therefore they never found their way into commercial developer products. There was nothing wrong enough with Metol and Phenidone that one would accept a stop less film speed plus relatively high fog, except if you are obsessed with creating a somewhat working developer from mostly natural ingredients (Sodium Carbonate is not edible, and neither is a developer made with significant amounts of Sodium Carbonate).

 

[elerion]

There is a good description of this in Grant Haist's "Modern Photographic Processing", highly recommended reading BTW, and quite a bit easier to read than T. H. James's "Theory of the Photographic Process".

Rudeofus, thanks for your summary.
Since you mentioned it, I never really knew if it is n=2 or n=3 for HQ (I've read both, and both seem reasonable as "number of double bounds between functional groups") and also if meta substitutions satisfy the Kendall-Pelz rule. We know they are not developers, but aren't they just n=1 developers according to the rule ?

 

[Rudeofus]

Since you mentioned it, I never really knew if it is n=2 or n=3 for HQ (I've read both, and both seem reasonable as "number of double bounds between functional groups") and also if meta substitutions satisfy the Kendall-Pelz rule. We know they are not developers, but aren't they just n=1 developers according to the rule ?

I stumbled over this same question a while back, and proper chemists told me the following:

A-(C=C)n-A' means A-A' for n=0, A-C=C-A' for n=1, A-C=C-C=C-A' for n=2, A-C=C-C=C-C=C-A' for n=3, ... Therefore Catechol would follow the Kendall(-Pelz) rule with n=1 or n=3 (depending on where you draw the double bonds on the benzene ring), and HQ would correspond to n=2. Resorcinol would not follow this structure for any n and is also not known to work as developer.

 

[elerion]

Once again, very informative.
Many references on the Internet seem to be just imprecise (at best).

 

[elerion]

Just out of curiosity, I've been testing a simple homebrew developer, just substituting coffee with tea. Same carbonate and ascorbic as Caffenol C-M formula. No restrainer.
I got a slightly lower pH than Caffenol C-M (10.20 vs 10.60), closer to that of Caffenol C-L. So I tried a semi stand development.
I got pretty nice negatives!

It seems that 20 teabags (of a cheap tea) per litre is close to Caffenol's activity, but still a less active.
I'd like to get raise pH 0.5 or so, see if it works faster.
I can get to it adding more soda, or leaving some ascorbic acid out.
Less ascorbic raises pH, but also lowers one dev agent concentration.
Any advice on how to proceed?

 

[Rudeofus]

Since your formula is already loaded with carbonate and ascorbate, it doesn't matter much which change you do. There is no magic truth to either amount. In a perfect world you'd have a bottle of 10-25% Sodium Hydroxide or Potassium Hydroxide available to raise pH as needed, and maybe some 10-30% Acetic Acid to lower pH.

 

[elerion]

Buffer capacity is not always symmetrical.
I supposed we needed better buffering capacity to resist to pH drops, than increases, because I thought that during development, the pH should drop, not raise.
But, after two test with two different batches, pH raised 0.1 after developing one 24 exposures roll.
Does it make sense?

 

[Rudeofus]

I have seen developers which go up in pH with use or aerial oxidation, but wouldn't dare a guess which developer is likely going to do this. With Caffenol you are completely on your own.

 

[elerion]

I did some more experiments, adding just 3 ml of Rodinal per litre to the tea-ascorbate developer.
It raised the pH a little bit, and accelerated development quite a lot (almost three times). Also some speed is gained. At least two rolls can be developed with 300 ml of working solution (the second one I developed was three days later - no sulfite used, airtight container - and needed some more developing time, but less than 15%).

As ascorbate is super-additive with p-aminophenol, I Just need to let out the tea, to see how the tea itself contributes to the activity and speed.

By the way, after adding p-aminophenol, the pH does go low, not up, after development.

 

[Rudeofus]

Well, now your developer experiments have gone full circle from Caffenol to Rodinal+Ascorbate. Not exactly sure where this is heading ....

 

[elerion]

Not really. Rodinal+ascorbate aims to improve Rodinal.
I'm using Rodinal just in a tiny amount (< 1+300) to see how it boost a tea-ascorbate developer.
The next step's goal is not testing a Rodinal+ascorbate, but letting out tea in the same formula (all the rest the same), to see if it (and how much) affects the output.

Heading where? To a good enough tea based developer, to use as an alternative to other commercial developers. Not to replace them, but to have more creative choices.
And in the meanwhile, learn things from experimentation.