He writes how to compose the ink in:
www.leonardodigitale.com
Codice ARUNDEL 170r
and
Codice Forster III 39 r.
Many thanks.

Iron gall ink is generally made from an iron (II) compound, and an aqueous acid. The iron compound is usually iron sulfate (FeSO₄) and the acid is usually tannic acid, extracted from various plant sources, although there are many recipes to make the ink.

The full chemical composition of the ink used by Leonardo is probably fairly complex, given that it was made from quite a few ingredients. The important chemicals are Fe₂⁺ ions and C₇₆H₅₂O₄₆ (tannic acid).

This website discusses iron gall ink in detail:
irongallink
irongallink-ingredients
irongallink-manufacture
historic recipes
chemical reactions

The website summarizes the ingredients, “Iron gall ink is primarily made from tannin (most often extracted from galls), vitriol (iron sulfate), gum, and water.”

I do not know Italian, so this is the best translation I could come up with (un-translated words are in italics). It appears to be a specific recipe for making iron gall ink.

Arundel 170r
(from translate.google.com)
Tartar, powder and apples zuchero much of one as the other limbic distila to: the effectiveness lentigine the first, second, and by the hair of blacks yellows, and in the wet this Florentine then you wash and dry the head, and dry and wet this

A pound of letargirio pionbo, 2 pounds of mortar alive, 3 ounces of gall, candied walnut green or seche 6 ounces, aseto strong bocali 6: bolire ago slow fire for half an hour, and felt as cola and warm, and co 'water wet this hair

Forster III 39r
I am afraid I could not come up with a reasonable translation of this one.

This is a very interesting question! While I can not be sure of the exact recipe that Leonardo used for the ink in his codices, there is a wealth of literature available on common recipes during that time that would have been prevalent throughout his lifetime. There are four main components to the Iron Gallus Ink recipe: tannin, vitriol (iron sulfate), gum Arabic, and water.

Ink is really just a suspension of a few ingredients in water: while the water provides the medium for the ink to flow and be dispensed, the gum makes the water slightly more viscous to improve the flow of the ink (reduces the blotchiness of the final product), and the tannin and vitriol are there to react together and provide the dark color that characterizes ink.

Tannin is a general term for chemicals that are important for tanning hides to make leather; tree galls (created by parasites that lay their eggs in the tree) have high tannin content which also contains the all-important tannic acid (C₇₆H₅₂O₄₆).

It appears that mostly oak was used for Iron Gallus Ink (abundant in Europe), the galls of which are produced by nesting wasps. Tannin can also be extracted from the bark of the tree as well. Vitriol is an umbrella term for mixtures of copper and iron salts.

In Iron Gallus Ink, the important chemical is iron sulfate (Fe(SO₄)). When the tannin and the iron sulfate are mixed in water and gum suspension, they form a larger molecular complex that is soluble in the water. Upon being exposed to air (i.e. when the ink dries as the water evaporates), the Fe₂ + cation in the molecular complex is oxidized to a Fe₃+ state, causing the formation of ferric tannate which is a darker pigment. Ultimately, making ink is just chemistry!

In summary, the 4 essential chemical components that make up Iron Gallus Ink are: tannin (which contains tannic acid), vitriol (which contains Fe(SO₄) that reacts with the tannic acid), water, and gum (that increases the viscosity of the ink).

I could give a long answer of my own to the query about Iron Gallus Ink, but better yet, I would refer Missine to
- irongallink

And perhaps for further detail
- irongallinkorg .

Do you mean iron gall ink? I wasn't able to find the exact chemical composition but it is made from tannins, chemicals in plants used to deter herbivores. It contains iron in an oxidized state (2+, eventually becoming 3+), and is acidic (tannins are acidic).

Wow - it's still sold today! You can find lots of info at this site:
Wikipedia Iron Gall Ink .