Measuring paint mixtures by the spoonful to shade a blue object
A spoon-measure method for compounding exact degrees of light and shadow
Continuing the third book of the treatise, Leonardo sets out a precise 'scientific' method for mixing paint: a small level spoon, sized to the scale of the work, measures out degrees of colour — for example three spoonfuls of black to one of white lead — so a tone of known quality can be reproduced without doubt. He then applies this to a blue object placed between a white wall and a dark one, compounding its darkest shadow from three spoonfuls of black and one of luminous blue. The passage closes by turning to the geometry of the object's form, drawing lines from the edges of the dark wall to the centre of a spherical body; a small labelled diagram at the foot of the page illustrates this construction.
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Measuring colour quantities with a level spoon
To work with sure and true science, Leonardo recommends a small spoon, only a little larger than an ear-spoon and scaled to the work, with rims of equal height. With it one measures level spoonfuls of pigment as grain is measured, so a shadow made of three degrees of darkness and one of lightness becomes three spoonfuls of black to one of white lead, a compound of certain quality.
Shading a blue object set between a light and a dark wall
Having prepared one white wall and one dark, Leonardo places a blue object between them that must carry the true shadows and lights proper to such a blue. He sets aside the pure blue that is to remain without shadow, then compounds three spoonfuls of black with one of luminous blue to make the darkest shadow.
Lines from the dark wall to the centre of a spherical body
The text asks whether the object is spherical, columnar, square or otherwise, and for a sphere directs lines from the extremes of the dark wall to the centre of the object. A small geometric diagram carrying letter-labels and a central point appears at the foot of the page to illustrate this construction.