Oil Paintings Lessons

Oil Paintings and Glazing is a technique that has been around since the 1500's. It is the application of very thin layers of paint. It is popular with formal painters that desire to achieve a "glowing effect" in their painting. Glazing oil paint, or even acrylic paint for that matter, will help your finished work of art to appear luminescent.
It is highly recommended to start with an underpainting. The way light works with glazing is that it travels in through the layers of thin glazes, hits the underpainting and bounces back out toward the viewer, creating a glowing appearance.
The main rule of thumb with glazing is to allow time for each layer to completely dry before adding another glaze. Patience is your number one tool for a successfully glazed painting.
Glazing Examples - Oil Paint
The students began by washing their canvas with a solid color. In this case, they used the color Raw Sienna in acrylic paint. A wash helps to messy-up the canvas so it's easier to begin on - rather than having to mark on a bright, white, clean canvas. They used acrylic for speed because it dries quickly. And, the acrylic they used was very watered down.
They each chose one object to paint, or a simple still life. One was a shoe, the other, a party hat. They each painted their simple still life in a monochromatic color scheme. This means using just one color on a value scale. They painted this part in Oil Paintings. This took a couple of class sessions to complete, an average of 4-6 hours to finish the underpainting.
Underpaintings can be created in any color, though the most popular colors throughout history are grayscale (from black to white) or a value scale of raw sienna, which helps to set charcoal and gives a beautiful glow through whatever is painted on top of it.
They allowed their underpaintings to completely dry for about a week.
Mixing the Glaze
Color theory is still important when choosing your glaze color. Whatever color you use will appear as if it were a piece of colored glass placed on top of a solid color. If you put blue over yellow, it will appear green (as in the background of the shoe painting). If you glaze red over blue it will appear purple (as in the example of the party hat painting).
Mix a tiny amount of oil paint with a larger quantity of linseed oil. Make sure to mix it very well so there are no chunks that can cause streaking in your painting.
Once it is mixed, apply it directly to the area you wish to glaze.  Keep in mind a glaze will alter your highlights. So, if you desire to have an area that is very white, either don't paint over it, or know that you will have to go back and use white on it at the very end of the painting process.
If you do not like your glaze color, remove it immediately with a soft rag and turpentine. 
If you are happy with your glaze, allow it to dry completely prior to applying another layer to alter the color again.
Some paints are better for glazing than others.  Look on the tube of paint at the transparency rating. Transparent colors are the best for glazing, however some may be considered "fugitive" colors, such as sap green, and may darken or lose their color over time.
Good luck!