I mix Coffee and Soda seperate, as it makes it easier to see if the Soda is completely dispersed.
150ml Water, 6 rounded Teaspoons Instant Coffee
200ml Water, 4 leveled Teaspoons Washing Soda
Mix all together, add 1/4 Teaspoon of Vitamin C
Let solution stand for about 5 minutes to clear microbubbles.
9:00 minutes at 20 degrees, fix and rinse as usual.