Keset Hasofer says it should be made from a combination of soot of oils or of pitch or of wax or similar to these, kneed it in gumi and add a little honey and we moisten it much and [then beat] it thin until one makes wafers.  Before the writing, one soaks them in gallnut juice or similar and he one writes with it. Indeed, in ancient times scribes would keep their reed pens in a pen-case together with the cakes of ink.

The sofer moistened the tip of the pen in water or gallnut juice then dipped it into the ink-cake, thus mixing his ink as he wrote. There are many other recipes in the Talmud. There is also a fair deal of argument over the kankantum as to whether iron sulphate should be used because of the section of the sotah than needs to be washed off.  Some scribes add a dash of honey or alcohol or vinegar. Basically whatever recipe is chosen, the ink has to be black and stay black as long as possible.  If it goes blue its no good, if it goes a reddish brown after a few hundred years that’s okay, but if it does this quickly or goes really red then it wasn't S"TAM ink and the work was never kasher.

Mordechai Pinchas