In oil painting there are basically two approaches, direct and indirect. Direct painting, also called alla prima (all at once) is basically finishing a painting all in one go, wet into wet (paint), usually, by layering on different passages of paint over a white or toned ground. Indirect painting is a technique where layers of paint are applied and allowed to dry, or in many cases so much time goes by that the last layer of paint has already dried (as in my case).
According to Virgil Elliott in his book Traditional Oil Painting (and I’m paraphrasing liberally) there are, basically, two schools of indirect painting, Flemish (Flanders) and Venetian. It’s interesting that most of the terms that come down to us are either French or Italian, but not Dutch. In Flemish painting they did a cartoon (drawing) and then transferred it to the white grounded canvas by poking holes in the drawing and overlaying the canvas with the perforated drawing and hitting it with a pounce bag full of charcoal (probably). Then they kind of connected the dots from pouncing, reinforced the drawing with linear painting sealing it with varnish that could, also, have been toned with a pigment, and called an imprimatura.
Oil painting comes to us; because, egg tempera had issues (like it dried too fast). The illuminated manuscripts of the previous medieval period were mostly done in egg tempera. Oil paint stays open longer (dries slower). Sometimes egg tempera was used in the under painting.
Then they painted over the dry vanish and with glazes using transparent dark pigments for the shadow areas, and blocked in large areas of color, both thinly. Then the edges, mid tones and large areas are worked more opaquely, and the highlights were added last, more heavily (impasto). They tended to paint on smaller wood panels with soft round brushes using less viscous (long) paint that had a high gloss finish.
The Venetian’s invented the use of canvas and stretchers in order to paint larger paintings for palaces and estates. They also used hogs bristle brushes and stiffer paint (short). The shorter paint was less glossy. Both techniques used glazing with transparent layers, but the Venetian style employed an opaque underpainting in what is called grisaille if done in grey, but they also used Venetian red mixed with white. The Venetians discovered that a lighter opaque layer could be scrubbed (scumbled) on top of the glazes. The effects of glazing and scumbling increased the range of light effects possible with oil paint.
There is also the semiglaze which can be used to alter the color of glaze at the same value (light to dark) of the under layer.
I would like to give a shout out to Virgil Elliot; because, even though the terms cartoon, imprimatura, grisaille, etc. are pretty out in the public domain, he does a great job of consolidating all this information into an understandable historical context.
So, if your mind is not, already, glazed over, what’s in a glaze? Glazing is a rather nuanced technique. Subtleties like mediums (solvents and bodied oils, or clear drying polyesters like alkyd) are mixed with transparent colors. Pigments come in several important differences, opaque and transparent, fast drying and slow drying, there are differences in the amount of oil in them (fat and lean), and thick or thin. If you are ignoring the subtleties, or don’t understand them (as I didn’t), things can go wrong and crack up. There is more to oil paint than fat over lean and thick over thin (but start the painting with the darks and shadows). These characteristics were referred to in another blog as Flexible, Fat and Fast. If you are interested in further reading it’s http://kaplanpicturemaker.com/tips__info/oil_painting