Casting recipe and a note on light and apparent size
Tartar-and-plaster mould mixture; the brighter object looks larger
A page of notes in mirror script. The first entry, headed 'for casting', gives a recipe in which burnt and powdered tartar mixed with plaster and cast makes the plaster set firm after firing, yet dissolve again in water. A following observation on optics states that of two objects at equal distance and size, the one more strongly lit appears the larger. A short separate note adds, cryptically, that 'holding the board is half a blow'.
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Tartar-and-plaster mixture for casting
For casting: tartar, burnt and pulverized and mixed with plaster and cast, causes the plaster to hold together once it has been fired; and afterwards it dissolves in water. The note reads as a working recipe for a mould material that can later be washed away.
Brighter of two equal objects appears larger
Among things of equal distance and equal size, the one that receives the stronger light will appear of greater size. Leonardo records the perceptual enlargement of brightly lit bodies.