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It is quite interesting to look at how these kitchen-table developers have evolved.Moments of inspired ingenuity, paired with a deep knowledge - sometimes, at other times one can speculate, sheer luck og just haphazard randomness that sort of worked anyway, until somebody saw it, refined it and madse it into something close to the "store-bought" versions.
As far as recipes goes, its my impression that anything that is given as a "scoop of this, and a dab of that" with no firm data, is based on very little actual knowledge and understanding.
My biggest eyeopener was Reinholds blog who offered true, measured recipes.
He has done a great work of standardizing this and deserver credit for that.
However the long hidden chemist in me, soon started to want to look under the hood, what is it that makes this recipe work, and work like it actually does, and that recipe to fail? In doing that I more or less automatically fell back on the classic chemistry I was thaught when I studied to be a chem. engineer many many moons ago.
In doing that I brushed off long forgotten tomes and decided to try to usort as many of the myths as possible.
Today we will look at concentration.
Most anyone will know that chemicals work better the more there are of them in a given volume og solvent.
Since our solvent is water, we need not concern us much over that, most people think they know everything there is to know about water....
The other chemicals however is interesting.
Most lay-people work out concentration as a percentage, and think that is all there is to it. For instance the standard recipe for Coffenol C-M:
Soda 54 gram
Vit C 16 gram
Inst. Coffe 40 gram
Water to a total volume of 1 litre.
It is fairly easy to establish the initial concentration of each of these :
Soda 5,4%
Vit. C 1,6%
Also Its very hard to predict anything from these numbers. We need to dig deeper.
These 3 chemicals have a very different chemical composition, coffe even have a nearly unknown chemical composition.
We need to base ourselves on atomic numbers, atomic weights and molecular weights.
This is not difficyult, but maybe a little unfamiliart to most people, so here goes:
Soda, Na2CO3 has a molecular weight of 105.998 gram rounded to 106 gram
Ascorbic acid which is our Vit. C has a molecular weight of 176,12 gram, or 176 gram
Coffe on the other hand is a mix of chemicals, since this was a living thing.
We are after one substance caffeic acid, which has nothing to do with coffeine the active ingredient to humans drinking coffe.
It is safe to say that caffeic acid must be a smallish portion of the total coffe weight, we know the molecular weight, and if we stipulate the percentage in the roasted beans to be no less than 10%, no more than 15% we have a base to work from.
Caffeic acid has a molecular weight of 180,16 gram or 180 gram flat, good enough for our purposes.
What is the importance of molecular weights? We use them to find a special form of concentration : if we mix a fluid with the exact molecular weight of a substance, we call that a 1 Molar concentration.
A 1 Molar concentration contains exactly the same number of atoms or molecules in the case of large molecules like ours.
Now the exact same number of molecules seems like a good idea, from that it is possible to deduce anumber of things : like how well a reaction goes, and the acidity, the pH number for instance.
If we look at our recipe again :
Coffenol CC-H
Soda 54 gram
Vit C 16 gram
Inst. Coffe 40 gram
1 gram Kbr (no influence on pH)
Water to a total volume of 1 litre.
we find the molarity of each ingredient :
Soda 54/106 = 0.50943M ~= 0.51M
Vit C 16/176 = 0.090909M ~= 0.09M
Coffe (40/10)/180 = 0.02222M ~= 0.02M
These molar concentrations is the base for pH calculations, the numbers are plugget into professional software, and pondering upon that gives some surprising results!
a single 0.51M solution of Na2CO3 gives a pH of 11.98
Mix that with 0.0909M of ascorbic acid and we have :
Soda 0,51M
Vit C 0.09M pH 10.85
Mix this with 0.022M of caffeic acid and we have :
Soda 0,51M
Vit C 0.09M
Caf. acid 0.022M pH 10.75
I think this is moderately interesting, pH is lowered one full unit by the vitamine and just a few tenths from the cafeine acid. That points to the fact that the vitamine is the more active ingredient, but is certainly no proof of that!
But this gets way more interesting when we study and disects both my very own inermediate recipe CC-I, and the "low pH" recipe CC-L! I can promise an eyeopener there, but that will have to wait.
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Lets look at Cofenol CC-I (intermediate)
Soda 35 gram
Vit C 13 gram
Inst. Coffe 40 gram
1 gram Kbr (no influence on pH)
Water to a total volume of 1 litre.
we find the molarity of each ingredient :
Soda 35/106 = 0.3302M ~= 0.33M
Vit C 13/176 = 0.07386M ~= 0.074M
Coffe (40/10)/180 = 0.02222M ~= 0.02M
a single 0.33M solution of Na2CO3 gives a pH of 11.89
Mix that with 0.07386M of ascorbic acid and we have :
Soda 0,33M
Vit C 0.074M pH 10.74
Mix this with 0.022M of caffeic acid and we have :
Soda 0,33M
Vit C 0.074M
Caf. acid 0.022M pH 10.61
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Lets look at Cofenol CC-L (low)
Soda 16 gram
Vit C 10 gram
Inst. Coffe 40 gram
1 gram Kbr (no influence on pH)
Water to a total volume of 1 litre.
we find the molarity of each ingredient :
Soda 16/106 = 0.1509M ~= 0.15M
Vit C 10/176 = 0.05681M ~= 0.057M
Coffe (40/10)/180 = 0.02222M ~= 0.02M
a single 0.15M solution of Na2CO3 gives a pH of 11.71
Mix that with 0.07386M of ascorbic acid and we have :
Soda 0,15M
Vit C 0.057M pH 10.44
Mix this with 0.022M of caffeic acid and we have :
Soda 0,33M
Vit C 0.074M
Caf. acid 0.022M pH 10.20
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Now hat happened here? Ph went down just a little, quite contrary to what has been said and expected! Why??
Well its simple, Soda is a quite capable BUFFER, it takes a large amount or a very small amount of soda in the water appreciably, it tends to keep pH stable.
At the same time we decreased the amount of ascorbic acid, this prevents the pH from coming down also, and the contribution from caffeic acid remains small.
Just look at the numbers :
Caffenol CC-H expected pH = 10.75
Caffenol CC-I expected pH = 10.61
Caffenol CC-L expected pH = 10.20
This was far, far above what was expected. From my school days I still remember how tricky it was to calculate pH in a 3-chemical mix with weak acids and bases, like here, fiddling with a slide rule, modern PC programmes makes minchmeat out of this!
However one still needs to understand what one are doing, this is probably the cause of the misunderstandings reported elsewhere.
One should hoiwever keep in mind that if one has the wrong soda or other things goes wrong these calculations will be far from the resuklting mix!
I was under the impression that pH, not actual amount of developer or concentration thereof, was tha main factor in this developer, I think I will change my mind about that.
Also I will reconsider and go back in my notes, my earlier failure with Cofenol CC-L must have been a flaw with the film, not a case of too low activity in the developer because of low pH.
Conclusion so far.
While CC-H remains the robust all-round alternative, CC-L is perfectly safe if mixed correctly, and should give excellent results, as demoonstrated by others.
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