The Painter in oil

Short Sittings. - This characteristic, and the steady change of position of the sun and
its effects on all the objects which are directly lighted by it, make it necessary, whenever
you are painting from nature out-of-doors, that you should not paint at one thing very
long at a time. The light changes pretty rapidly; at high noon it only takes a few moments
to exactly reverse the light. It is seldom that you can do any just study for more than an
hour or an hour and a half at a sitting. Some men do work two or three hours, but they
are not studying justly all that time; for that which was light is dark three hours later,
and any true study of value and color is impossible under these conditions. Of course on
gray days this is less marked, but you must suit your sittings to the time and facts.
It would be better if you had more canvases, and worked a short time on each, and
many days on all. You would have the truest work.
Monet works never more than a half-hour on one canvas; but when he starts out he
takes a half-dozen or more different canvases, and paints on each till the light has
changed. Theodore Robinson seldom worked more than three-quarters of an hour, or at
most an hour, on one canvas; but, he worked for twenty or thirty days on each canvas,
and sometimes had a single canvas under way for successive seasons.
Any man who would truly study for the just value and note of color must, work more
or less in this way when he works out-of-doors.