Dissolve 50g Sodium Carbonate anhydrous (or equivalent) in 5 liters water and store in a jerrycan. This is a 1% solution, if you use other units, calculate 1% of the weight of the water quantity.
Now, when preparing for instance 500 ml of working solution, dissolve 10 g soluble cheap coffee, not arabic, not decoffeinated, in 200 ml water. After the coffee is completely dissolved, start adding the 1% solution of Soda until you reach 10,4-10,6 pH. Complete with water to make 500 ml if needed.
I think this is very practical and allows you to adapt the soda amount according to the acidity of the coffee used. For instance, if you use 200ml coffee solution and 300ml soda solution, you have 3g/500ml what is 6g/liter instead of just 5g. As a matter of fact, the real amount of soda is between 5 and 6 g, when using 20g/liter of coffee.
|Polypan F + Caffenol Black (and Photoscape)|