2428. Make two sticks of strong wood, neither too thick nor too thin, about a foot long; let them be well rounded at the top and bottom, and nicely smoothed. Then have your paste in the glazed basin into which, add to it a porringerful of lye, moderately warm; and with these two sticks, one in each hand, turn and squeeze and knead the paste thoroughly, exactly in the manner that you would knead bread.
2429. When you see that the lye is thoroughly blue, pour
it into a glazed basin; take the same quantity of fresh lye, pour it
over the paste, and work it with the sticks as before. When this lye is
very blue, pour it into another glazed basin, and continue to do so for
several days, until the paste no longer tinges the lye.
2430. Then throw it away, it is good for nothing. Range
all the basins before you on a table in order, that is to say, the
first, second, third, and fourth ; then beginning at the first, with
your hand stir up the lye with the azure, which by its weight will have
sunk to the bottom, and then you will know the depth of color of the
azure. Consider how many shades of the azure you will have, whether
three, or four, or six, or what number you please.
2431. At this point I will break off copying out Cennini’s directions for making ultramarine blue, because I am sure that when I reached the point of telling you about how you have to mix lye with the powder, and then mix it for several days, you probably lost interest.