Monday, July 15, 2013

Caffernal, first working recipe

I may now announce the first working Caffernal and its recipe is following, but please understand what I mean. To start, let us consider the balanced equation of the reaction between Ascorbic Acid and Sodium Hydroxide to give Sodium Ascorbate and Water:

C6H8O6 + NaOH → C6H7O6Na + H2O
176 g  + 39 g = 197 g + 18 g

The complete reaction needs 4.5 times (176/39) Ascorbic Acid in relation to Sodium Hydroxide.

But we don't want the complete reaction because there is a risk of surplus of Sodium Hydroxide that will give a high pH, or a risk of low pH that combined with coffee can go acidic and no development will take place. After some disasters, my starting point was fixed at 3 parts of Ascorbic Acid in weight for 1 part of Sodium Hydroxide and I end with a basic pH of 11,6, but still to high for ascorbate developer. So, I added coffee as acid to lower th pH to 10.6. And here is the whole procedure:

Preboil 1 liter water for 10 minutes and let cool. Add 5 g Potasssium Metabissulfite as Oxygene scavenger. Then use just 100 ml of this water in a beaker and dissolve 60 g Ascorbic Acid in it. Then put the beaker in a bowl with cold water and add 20 g Sodium Hydroxide and stir (don't forget gloves and googles). Pour some more of the cold preboiled water, say, 50 ml. The color of the mixture is light yellow. At the end of the solution measure the pH which will be about 11,6. Now weight about 60 g soluble coffee and go on adding to the soup and measure the pH. When you reach 10,6, more or less, stop. Add 5 g Potassium Bromide as anti-fog (it is enough). Add some more of the preboiled water to make 250 ml and store in an amber bottle of 250 ml. You have prepared the stock solution of Caffernal.

According to my experiments, for each 100 mg Sodium Hydroxide more than the necessary, you will have to put more 1 g of coffee. Suppose that by mistake you putted 2 grams more of Sodium Hydroxide, this will need 20 g coffe to neutralize it. So, be careful and don't waste resources, unless you want to change the proportion Ascorbic Acid to Coffee for a developer with other properties, more grain, more contrast and so on.

And so we have constructed a developer that can be used very diluted. I have been using it in dilution 1:50 and I need some 60 minutes at 25ºC to develop well the film Ilford FP4.

Have fun with Caffernal!

Note: For better understanding, I add a small explanation in red.

2.nd Note: Sodium Ascorbate has a pH between 7.4 and 7.7. Without a surplus of alkali it will not develop.

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