|Distilled water||200 mL|
|Potassium metabisulphite||1 g|
|Hydrochloric acid, 1N||25 mL|
|Activated charcoal (powder)||1 g|
Bring the water to boiling.
Remove from the heat and add the dye (be careful of foaming).
Cool to 50° C, add the hydrochloric acid and mix well.
Cool to room temperature, and add the metabisulphite.
Shake thoroughly and leave overnight or longer.
If the solution is discoloured (brown), add the activated charcoal, shake well and immediately filter.
Store at 0-5°C in a tightly stoppered bottle.