On painting: bodies should not be outlined
With a red-chalk tree trunk, two profile-shaping devices, and a rule on circle proportion
Under the heading 'On painting', Leonardo argues that the colour of a lit body partakes of the colour of what lights it, and that the boundary of a body is a surface of no thickness, so a painter should not draw bodies with outlines, especially for objects smaller than life. A red-chalk tree trunk at the top notes that branches make a swelling base where they leave the trunk (a b c d). Lower on the sheet, two drawings of a 'sagoma' (a profile-shaping device) show its driving teeth guided by curved channels, while a right-margin note gives a rule for making two circles in the same proportion as two squares.
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Boundaries have no thickness, so a painter should not outline bodies
The colour of an illuminated body partakes of the colour of whatever illuminates it. The boundary of a body is a surface belonging neither to the body nor to the surrounding air but interposed between them, and its lateral edge is a line of invisible thickness. Therefore the painter should not surround bodies with lines, above all in things smaller than life, whose very parts become invisible at a distance.
A 'sagoma' whose driving teeth run in curved channels
Two drawings show a sagoma, a mechanism for shaping a profile. Leonardo notes that its driving teeth are guided by curved channels.
Two circles in the same proportion as two squares
The proportion between two circles is as that between the squares built on their diameters. Make two squares in any proportion, then draw a circle on the side of the larger square and another on the side of the smaller; by the converse of the first proposition the two circles stand in the same proportion as the two squares.
Swelling base where branches leave the trunk (a b c d)
A red-chalk study of a tree trunk. Where the branches separate from the trunk they always form a base with a swelling, as shown at a b c d.