CHAPTER VI: VEHICLES AND VARNISHES
A vehicle is any liquid which is mixed with the color to make fluent. The
vehicle may be ground with the pigment or mixed with it on the palette,
or both. Oil colors are of course ground in oil as a vehicle; but it is often
necessary or convenient to add to them, in working, such a vehicle as
will thin them, or make them dry better. Those which the thin ore
render more fluent the paint are oils and spirits; those which make them
dry more quickly are “dryers” or “siccatives.”
All vehicles must of necessity have an effect on the permanency of the pigments. Bad
vehicles tend to deteriorate them; good ones preserve them.
Oils. - The most commonly used oils are linseed and poppy oil. They are neither of
them quick dryers, and are usually mixed with sugar of lead, manganese, etc., to hasten
the drying. These have a tendency to affect the color; but if one will have recourse to
none but the pure oils, he must be patient with the drying of his picture. For this reason
it would be well to use vehicles with the colors on the palette as little as possible - and
that is against thin and smooth painting.
Oil has the tendency to turn dark with time, thus turning the color dark also. The only
way to reduce this tendency is to clarify the oil by long exposure to sunlight. The early
German painters used oil so clarified, and their pictures are the best preserved as to
color of any that we have. But the drying is even slower with purified oil than with the
ordinary oil.
It would be best, then, to use oil as little as may be in painting, and if you need a dryer,
use it only as you actually need it in bad drying colors, and then very little of it.
The essences of turpentine and of petroleum may be used to thin the paint, and are
preferable to oil, because they have less darkening tendency. They do not, however, bind
the color so well, and the paint should not be put on too thinly with them. Usually there
is enough oil ground with the pigment and as it comes in the tubes to overcome any
probability of the paint scaling or rubbing when thinned with turpentine, but in the
slow-drying, transparent colors there will be a liability to crack. Moderation in the use of
any and all vehicles is the best means of avoiding difficulty.
Use vehicles only when you need them, not habitually, and then only as much as there is
real need of. If use oil, use the lighter oils, and expect some darkening in time. Prefer
turpentine to oil, and expect your color to dry rather “dead,” or without gloss, by its use.
If you intend to varnish, that is all right. If you do not intend to varnish the picture, keep
the color is near the pure tones as you can. The greater the color, the more the “dead” or
“flat” drying will make it look colorless.