To preserve the colors fresh and clean in painting ; it must be done by laying in more colors, and not by rubbing them in when they are once laid ; and if it can be done they should be laid just in their proper places first, and not be touched again because the freshness of the colors is tarnished and lost, by mixing and jumbling them together ; for there are certain colors which destroy each other by the motion of the pencil when mixed to excess.
For it may be observed that not only is the brilliancy as well as freshness of tints considerably impaired by indiscriminate mixing and softening ; but if colors be too much worked about with the brush, the oil will always rise to the surface and the performance will turn comparatively yellow in consequence.
Never give the least touch with your pencil until you have present in your mind a perfect idea of your future work.
Paint at the greatest distance from your sitter, and place your picture occasionally near to the sitter, or sometimes under him so as to see both together.
In beautiful faces keep the whole circumference about the eye in mezzotinto, as seen in the works of Guido and the best of Carlo Maratti.
Endeavor to look at the subject or sitter before you, as if it was a picture ; this will in some degree render it more easy to be copied.
In painting, consider the object before you, whatever it may be, as made out more by light and shadow, than by lines.
A student should begin his career by a careful finishing and making out of the parts, as practice will give him freedom and facility of hand ; a bold and unfinished manner is generally the habit of old age.
Let those parts which turn or retire from the eye be of broken or mixed colors, as being less distinguished and nearer the borders.
Let all your shadows be of one color; glaze them till they are so.
Use red colors in the shadows of the most delicate complexions, but with discretion.
Contrive to have a screen with red or yellow color on it to reflect the light in the sitter's face.
Avoid the chalk, the brickdust, and the charcoal, and think on a pearl, and a ripe peach.
Avoid long continued lines in the eyes, and too many sharp ones.
Take care to give your figure a sweep or sway, with the outlines in waves, soft and almost imperceptible against the background.
Never make the contour too coarse.
Avoid also those outlines and lines which are equal, which make parallels, triangles, &c.
The parts which are nearest to the eye appear most enlightened, deeper shadowed, and better seen.
Keep broad lights and shadows, and also principal lights and shadows.
Where there is the deepest shadow, it is accompanied by the brightest light.
Let nothing start out or be too strong for its place.
Squareness has grandeur; it gives firmness to the forms, a serpentine line in comparison appears feeble and tottering.
Anonymous, The Hand-Book of the Elements of Painting in Oil, 1842, (Clarke and Wilson, London), pp. 49 - 53.