Clear oil for painting colours; recipe for artificial pearls
Purifying nut and seed oils with camphor, and dissolving pearls in lemon juice
The sheet is filled edge to edge with Leonardo's mirror-hand and carries a continuous set of workshop recipes for a painter's materials. The first notes explain how to draw off a clear, crystal-like oil from seeds and nuts for grinding colours, why such oils turn yellow, and how a little melted camphor keeps the oil from thickening. A further passage describes changing the lye and water in which crushed nuts are steeped until it runs clear before letting them decay. A final recipe, headed 'To fuse pearls', tells how to dissolve small pearls in lemon juice, dry them to powder, bind the powder with beaten egg white, and burnish freshly formed pearls on a small lathe.
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Drawing off a clear oil for grinding colours
The oil is let to separate from a milky water and run into the neck of a flask, where it becomes clear as crystal and is used to grind colours. Every impurity and viscosity stays behind with the water. Leonardo adds that oils from seeds or fruits are naturally very clear and only yellow when heat is not properly kept from them.
Why painting oil changes colour; camphor to prevent thickening
The change oil undergoes in painting is blamed on a subtle sap from the husk enclosing the nut, which mixes with the oil and penetrates over all the colours, making them alter. To keep the oil good and prevent it thickening, Leonardo says to add a little camphor melted over a slow fire and mix it well, so the oil never hardens.
Steeping crushed nuts in lye and water
Nuts left in lye for six hours can tint the oil and make it dark, so the lye should be changed every six hours until it comes out clear, then replaced with clear water treated the same way. Only then are the nuts left to decay before the rest of the process is followed as described above.
