A long time ago when I had mentioned I wanted to try making iron gall ink at home, fellow FPN member and iron gall ink legend Pharmacist recommended a recipe from this report which is consistent with ingredients he listed in his inks. He specifically told me that the trickiest and most expensive part was getting the super high purity aniline blue dye in order to prevent precipitation. Pharmacist was a great guy and he made amazing inks. I think this recipe was probably the basis of his famous urkundentinte blue black ink and one day, I hope to try to make it myself. Anyway, in case anyone else is interested, here is the recipe below:
Standard Writing Ink
Tannic acid 11.7 Grams
Gallic acid crystals 3.8 Grams
Ferrous sulphate crystals 15.0 Grams
Hydrochloric acid,dilute,U.S.P 12.5 Grams
Carbolic acid(phenol) 1.0 Grams
*Dye (C.I.707;Sch.539) 3.5 Grams
Water to make a volume of 1liter at 20° C (68° F).
*soluble blue (aka aniline blue)
Thank you for this recipe, which in a way confirms the feasibility of my recipes.
As you can see the starting point for both these inks is the couple gallic acid/iron sulphate to obtain the ferro-gallic basis, which is combined with a dye (which is used to obtain the blue colour which is necessary to see what you are writing before the ink turns black).
There is then also an acid ingredient (acetic acid, tartaric acid or HCl), the added phenol is the preservative (missing in my recipes, but I would add some to mine too). The proportions between the ingredients also look right!
I'd bet anything that any of these three recipes work!
You are right in saying the dye should be as pure as possible.
Not quite sure what the dye you mention exactly is but google comes up with some interesting info...