Mirror Alloy; Light Eating into a Body's Shadow
A tin-and-copper recipe for mirror metal, with two rules on the edges of shadow
A short note groups a foundry recipe with two rules of shadow. For mirrors, Leonardo prescribes 30 parts of tin to 100 of copper: first purge both metals, cast them into water to make grains, then melt the copper and add the tin. Two following statements observe that a luminous or illuminated body bordering a shadow cuts away as much of it as it touches, so the extremities of a body's shadow diminish wherever a lit field reaches them. A number, 3871, is written at the top of the leaf in a later hand.
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Recipe for mirror metal: 30 tin to 100 copper
For mirrors, Leonardo gives an alloy of 30 of tin to a hundred of copper. He directs that both metals first be purged and cast into water to make grains, then the copper melted and the tin added on top of it.
A lit edge cuts into the body's shadow
A luminous or illuminated body that borders a shadow cuts away as much of that shadow as it touches. Accordingly, as much is lost from the extremities of a body's shadow as is reached by a luminous or illuminated field.