Squares equal to curved figures, and a recipe for false jasper
Quadrature of two-curved-sided figures and triangles, with a craft recipe for imitation hardstone
Most of the leaf works on turning curved-sided figures into equal squares: parallels are set in rational (double, triple) proportion, a square is shown equal to a lune-like figure, and the added curved portions are proved to double successively from one figure to the next. Curved triangles built inside a right angle are shown to behave in the same doubling way while remaining equal to the first, one-curved-sided figure. In the left margin Leonardo adds a wholly separate craft recipe for imitating jasper, chalcedony and agate by coating broken paste and binding it in egg white and isinglass, tinted with walnut juice.
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A square equal to a two-curved-sided figure
Taking the square a b c d equal to c e d f, Leonardo adds the portion c g d and removes it from the second square, restoring it on the opposite side with the portion e h d, which is double the first. Half restores what was taken and half makes the second square equal to the first plus its added portion.
Curved triangles doubling in curvature
Triangles built inside the right angle on equal bases, meeting at its vertex, have their curvatures double one another in succession, yet all remain equal to the first triangle, which has only one curved side.
Parallels in rational proportion
Arrange the parallels a b c d to the parallels c d e f in rational proportion, such as double or triple, and the resulting portion will be sub-double or sub-triple accordingly.
Recipe for imitation jasper, chalcedony and agate
Coat each piece of broken paste in a white coating so it looks like fixed chalcedony, then bind it in a jelly of egg white and isinglass, drying it layer by layer. Adding walnut juice to the glue and egg white makes it look like agate.