## Saturday, June 22, 2013

### Maths again!

As you know from reading before, I have been studying the general purpose developers with Metol and Hydroquinone, the so called MQ developers and I am now proposing a family of such developers, having several of them in account. I propose the following general expression to calculate a MQ developer, with a small deviation from what I proposed before:

Metol + hydroquinone = K g/liter
Sodium Carbonate = 50 - A x Metol g/l
Sodium Sulfite = 100 - B x Hydroquinone g/l
Potassium Bromide = 1 to 3 g/l

Anyone may estimate the right values for K, A and B. I could also have choosen other maximums for carbonate and sulfite but 5% and 10% seem to be commonly accepted for baths where they appear alone. The other parameters, K, A and B I leave to individual choice. I am going to start with K=10, A =6,67 and B=10.

I assumed that the sum of developing agents is a constant, developer using only hydroquinone needs only sodium carbonate (50g/l) and developer using just metol only needs sodium sulfite (100g/l).

Let's make a developer respecting the expressions with my parameters for K, A and B.

I choose Metol = 3 g/l, so Hydroquinone will be 7g/l. Sodium Carbonate will be 50-6,67x3=30g/l and sodium sulfite will be 100-10x7=30g/l too.

Recipe:

Metol - 3 g/l
Hydroquinone - 7g/l
Sodium Carbonate - 30g/l
Sodium Sulfite - 30 g/l
Potassium Bromide - 1 g/l

This developer may be called MQ371.