They are discussing the traditional gesso recipe used for water guilding. In English the term gesso is used to refer to the entire mixture, while in your list of terms (gesso, polvere di piombo bianco, bolo armeno) gesso would be "chalk" in English.

The mixture is usually just called "gesso" but you can also say "gesso mixture" or "gesso recipe".

http://www.jcsparks.com/painted/Gesso_Supplies.html

http://www.assoc-restorers.com/r-articles/gessbind.html

If you search for "water gilding" and "gesso" you will find lots of useful links.