The mysterious recipes for making the special ink used in the writing of mezuzot, tefillin and Torah scrolls sound like they come from one of the dusty old tomes of Potions Master Horace Slughorn, of Hogwarts renown. One might ask, “What’s wrong with using a Bic retractable ball-point goose quill?”

What’s clear in our tradition is that Moshe was told by G-d at Sinai that these holy items must be written with an ink called de’yo. It’s also clear that this de’yo must be black and must have staying power. The Zohar indicates that ideally its ingredients must derive from plants. Over millennia the technology used to achieve these outcomes has changed, but the principles remain the same.

From the Dead Sea scrolls and ancient tefillin analyzed using a cyclotron at UC Davis we can see that originally scribal ink was carbon-based. Soot was gathered from burning vegetable fats, mostly olive oil. Charcoal dust was produced by burning vegetable matter such as beech trees or cedars. Often, a glass plate was suspended over the burning materials, and the gathered soot was scraped off for use.

Durability was achieved by adding oak gall-nut powder, a substance rich in tannic acid, to “bite” into the parchment. The galls are formed when a gall wasp lays eggs on the leaves of oak trees. The hatched larvae feed upon the tree, secreting an irritant that prompts the tree to create a growth “nut” around the larva. This substance is still an important part of scribal ink today.

A gummy substance (now, gum arabic) was also added to keep all the ingredients evenly suspended in solution, improve the ink’s even flow from the reed or quill, and keep it from bleeding into the surface of the parchment. It also increases the brilliancy and gloss of the ink. Unfortunately, with time this substance dries and may cause the letters to crack.

Over the centuries the secret of producing a durable ink made from carbon black has been lost. The Talmud records a halachic controversy regarding adding a chemical blackening agent (vitriol: ferrous sulfate) into the mix. Although the classic halachic sources recommend refraining from adding this ingredient, contemporary authorities have allowed its use, as carbon-based ink alone is not a practical option.

Scribal ink is not holy, but all the ingredients involved in the production of mezuzot and other holy items must be kosher, even though they are not consumed. Some researchers have asserted that commercial inks may contain problematic ingredients such as glycerin or shellac and are not an alternative to a traditionally made product for that reason alone. So, make sure your retractable goose quill is preloaded with the right stuff.

• Sources: Shulchan Aruch O.C. 32:3 and Y.D. 271:6

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