Continued excerpt from “Il Libro dell’Arte” or “The Craftsman’s Handbook” (Translation by D. V. Thompson,. Pages 36-37). 15th Century handbook for artists.
“It is true that the fine kind is more useful in illuminators, and for making draperies with lights on them. When you have this powder all ready, get six ounces of pine rosin from the druggists, three ounces of gum mastic, and three ounces of ne wax, for each pound of lapis lazuli; put all these things into a new pipkin, and melt them up together. Then take a white linen cloth and strain these things into a gazed washbasin. Then take a pound of this lapis lazuli powder, and mix it all up thoroughly, and make a plastic of it, all incorporated together. And have some linseed oil, and always keep your hands well greased with this oil, so as to be able to handle the plastic. You must keep this plastic for at least three days and three nights, working it over a little bit every day; and bear in mind that you may keep it in plastic for two weeks or a month, or as long as you like. When you want to extract the blue from it, adopt this method. Make two sticks out of a stout rod, neither too thick nor too thin; and let them each be a foot long; and have them well rounded at the top and the bottom, and nicely smoothed. And then have your plastic in the gazed washbasin where you have been keeping it; and put into it about a porringful of lye, fairly warm; and with these two sticks, one in each hand, turn over and squeeze and knead the plastic, this way and that, just as you work over bread dough with your hand, in just the same way, . When you have done this until you see your lye is saturated with blue, draw it off into a glazed porringer. Then take as much lye again, and put it back in on to the plastic and work it over as these sticks as before. When the lye has turned quite blue, put it into another porringer…and go on doing this for several days in the same way until the plastic will not longer color the lye; and then throw it away, for it is no longer any good. Then arrange all these porringers in front of you on a table, in series; that is, the yields, first, second, third, fourth, arranged in succession; and with your hand stir up in each the lye with the blue which, on account of the heaviness of the blue, will have gone to the bottom; and then your will learn the yields of blue. Weight the question of how many grades of blue you want; whether three, four or six, or however many you want; bearing in mind the first yields are the best, just as the first porringer is better than the second. And so if you have eighteen porringers of the yields and you wish to make three grades of blue, you take six porringers and mix them together, and reduce it to one porringer; and that will be one grade…but bear in mind that if you have good lapis lazuli, the blue from the first two yields will be worth eight ducats an ounce.* The last two yields are worse than ashes: therefore be prudent in your observation, so as not to spoil the fine blues for the poor ones.” To be continued tomorrow…
* My research on the value of a 15th century ducat (as I am a nerd for context): A ducat was the internationally accepted gold currency produced in Venice (it had about 3.5 grams of gold in each coin). Some websites post 1 ducat as the equivalent to $150 USD. Today’s monetary equivalent for a 15th century ducat is greatly contested and some believe it could be worth $250. Leonardo made about 50-100 ducats a year, and at the end of life had some years that he made approximately 400 ducats. In 1453 Medici had a wealth of 200,000 ducats.
The pictures included in the post below illustrate Cennini’s process! They are from Randy Asplund’s webpage concerning book illumination techniques. Here is the link:
Asplund describes Making the 15th century style Schiff Book, including great process pictures and materials. It is a great website!
Materials needed for creating blue paint to illuminate books
Grinding blue and turning it into a fine powdered pigment
A 15th century porringer