Here's the first rule (yes, in art rules are for breaking, but you have to understand the rule before you can break it most effectively)
Fat Over Lean
All mediums are fat, all opaque pigments without medium are lean. You want to paint opaquely first, with little or no medium. In subsequent layers you can move to using more medium because the oil will soak through to the first layer. Also, you don't want the under layer to dry slower than top layer as this will result in buckling and cracking.
The basic elements of glazing are pigment and medium. We'll start with the medium first.
Mediums can be as individual as your brush strokes, so there's no "true" formula. However, there are a few rules of thumb that you want to keep in mind.
- Never use Damar Varnish in your medium. If your painting is ever restored, they will remove the final varnish, and in doing so all of the varnish in your piece will break down. Meaning each layer will separate and your painting will disintegrate.
- Too much solvent in your medium will cause your pigment to break down, destroying your color and texture. One should never use more than 50% solvent.
- Certain oils tend to yellow more over time, so you definitely don't want to use vegetable oil. Stick with refined oils: linseed, poppy seed, walnut, spike oil.
(I recommend Gamsol instead of turp as it is safer and has no odor)
Easy Formula: 1/2 Refined Linseed oil, 1/2 Turpentine (vary quantities according to viscosity that you want) This is pretty quick drying and good for sketching and painting fast. However, it's not great for layers of delicate color - too much solvent. 2/3 oil, 1/3 solvent is much better for that purpose.
Vincent Desiderio's formula: 1/3 Venetian Turpentine, 1/3 Sun-thickened Linseed Oil, 1/3 turpentine
Adrian Gottlieb (which he says was taught to him by "Scott" at Charles Cecil's Studio): 1/2 Sun-thickened walnut oil, 1/4 Canadian Balsam, 1/4 Turpentine
There are three basic types of glazes:
1. Traditional glaze: a transparent pigment diluted with medium, color will become warmer.
2. Velatura: a glaze with a color which is lighter in value than the under layer and is semi-transparent. More simply put: it has white in it. This will cool off the color
3. Scumbling: an opaque kind of glazing produced by loosely dry brushing one color over another so that the under color shows through. There is no set rule here for temperature change as this depends upon the pigments, but generally if the value of the pigment is lighter than the under layer it have a cooling effect, darker will have a warming effect. This is great for optical blending, where you do not actually blend colors to produce a third color, but they look blended from a distance.
Transparent Glaze Palette
It's important when glazing to know the transparency or opacity of the pigment, as this will affect your color temperature and how you work with it. Different pigments have different abilities. Due to the strength and intensity of these colors, painters only need to mix a small amount of color with a suitable painting medium to produce a rich and vibrant glaze.
Indian Yellow — warm yellow makes painting look lit by sunlight
Transparent Orange — warm orange
Perylene Red — cool red with yellow undertone
Quinacridone Red — cool red replacement for Alizarin and makes high key tints
Quinacridone Magenta — cooler high key red
Quinacridone Violet — clean, warm violet
Dioxazine Purple — cold purple that can be used for a black
Manganese Blue Hue — cool (leans toward green) transparent blue
Phthalo Blue — 20th century replacement for Prussian Blue (also slightly greenish)
Phthalo Green — cold, dark green with great transparency and tinting strength
Phthalo Emerald — warmer, more natural looking Phthalo Green
In addition to Transparent Glaze Palette, these colors provide the abstact painter with a unique set of visual possibilities:
Mono Orange — clean, bright semi-transparent color, masstone of Cadmium Orange
Mars Black — dense, strong mark making black
Black Spinel — only black with neutral masstone and tint, dries matte
Hansa Yellow Deep — golden yellow, semi-transparent
The beauty of oil paint as apposed to acrylic is it's flexibility. There are five basic paint consistencies that you can use that will dramatically change your results. The more medium you add to your pigment, the more transparent it will become.
Impasto - thick textured paint application (Lucien Freud)
opaque - flat, even paint
semi-opaque - slightly transparent
These relate to the visual effect you want to produce.
Most of the old masters stayed in the semi-transparent, semi-opaque range with areas of Impasto and limited glazes.
Alex Katz paints completely opaque - which reinforces the flatness of his paintings.
*For an old master technique, here's a good rule of thumb: Shadows lean towards transparency, light mass is more opaque. This helps to reinforce the way light functions.
Here's a great exercise that Stephen LaRose recommended:
The most successful lesson that I had in glazing went this way:
I handed out, as homework, swatches that the students had to match. I didn't tell them that the swatches had an order.
There was a uniform color swatch, much like a paint chip (here the students simply honed their mixing skills)
There was a swatch that was the first color scumbled with medium to show the white of the canvas peaking through in an organic and random way. This was a technique lesson.
There was a third swatch that had a warm glaze over a version of the second swatch.
Then a fourth swatch with a cool glaze over the third swatch.
Four levels of optical confusion is all that most rookies can handle.
And another great exercise from me:Light Temperature and Form
Or a similar technique also from me:
Cover your entire canvas with a wash of any transparent pigment, Castle Earth, Transparent Red Oxide, Indian Yellow (I prefer more neutral colors, but chromatics like Pthalo Blue or Dioxazine Red work too). Paint into the "sauce" with only white to model the values. This is also great for beginners because it helps them to see how their alla prima technique relates to glazing and how a wet glaze will change their color.
Or a similar technique also from me:
Make a charcoal drawing. Dilute yellow shellac with denatured alcohol. Spread this mixture over the drawing with a large squeegie and let dry (should take around 30 min.) You can then cover this with a glaze and paint with oils into the glaze on top of the drawing (which is completely preserved) - this produces a very interesting effect.
You can find each of these above.
Highlight: cooler than light mass
Light Mass: warm
Shadow: Warmer than turning, but cooler than light mass
Core Shadow: cooler
Reflected Light: Always warmer than core shadow, but depends upon the color reflected.
*note - the color and temperature of the flesh is greatly dependent upon the color of the background. Also chromatic intensity in the background influences chromatic intensity in the flesh.
Vincent Desiderio likes to use a single unifying glaze over his whole painting. He feels that this helps to set a mood or atmosphere. Many artists use glazes for local color. Some leave them as is, and some modify them by painting back in wet into wet.
If you have any questions, feel free to ask.