Boil 19 parts water water in an old pot that you don't mind staining. Stir one part borax into it as you heat it.
Stir in two parts of gum shellac until it dissolves. Gum shellac, also known as gum lac, is a gummy excretion traditionally used as shellac. Nowadays, other compounds are used for most shellac, but they may not work well in this ink. Make sure to get the right stuff.
Let the water cool. Filter it through a coffee filter or some other kind of filter paper into a mason jar. Set it aside for now.
Mix one part gum arabic into two parts water. Stir or shake it around until it dissolves.
Pour the gum arabic and water into the mason jar with the first solution. Add one part powdered indigo. Cover the jar and shake it until everything dissolves.