The process of oil painting varies from artist to artist,
but often includes certain steps. First, the artist prepares
the surface. Although surfaces like linoleum, wooden panel,
pressed wood, and cardboard have been used, the most versitile
surface is canvas. While many famous paintings were painted
on panel (Da Vinci's Mona Lisa), the size of the work was
limited by weight and the thickness of the wood. Stretched
canvas, on the other hand, only depended on the width of the
roll fabric and could be unstretched for easier transportation.
Traditional artists' canvas is made from linen, but the less
expensive cotton fabric has gained popularity. The artist
first prepares a wooden frame called a “stretcher".
The canvas is then pulled across the wooden frame and tacked
or stapled tightly to it. The next step is for the artist
to apply a ground (or size) to isolate the canvas from the
acidic qualities of the paint. Traditionally, the canvas was
coated with a layer of rabbit skin glue and primed with subsequent
layers of finely ground chalk (or marble dust) and rabbit
skin glue. Later the process was changed to a sizing of rabbit
skin glue with subsequent layers of white priming (gypsum,
chalk, barium oxide, titianium(IV) dioxide mixed with linseed
oil). Modern gessos are made of titianium dioxide with an
acrylic binder and are not "real" gessos in the
true sense of the word. The artist might apply several layers
of gesso, sanding each smooth after it has dried. Sanding
the primed surface is important to roughen the generally slick
surface so the subsequent layers of oils will properly adhere.
Next the artist might sketch an outline of their subject
prior to applying pigment to the surface. “Pigment”
may be any number of natural substances with color, such as
sulfur for yellow or cobalt for blue. The pigment is mixed
with oil, usually linseed oil but other oils may be used as
well. The various oils dry differently creating assorted effects.
Traditionally, an artist mixed his or her own paints for each
project, but in the late 1800’s paint in tubes became
available. Artists then could mix standard colors easily to
create subtle variations of hue.
The artist most often uses a brush to apply the paint. Brushes
are made from a variety of fibers to create different effects.
For example, brushes made with hog’s bristle might be
used for bolder strokes. Brushes made from miniver, which
is squirrel fur, might be used for finer details. Sizes of
brushes also create different effects. For example, a "round"
is a pointed brush used for detail work. "Bright"
brushes are used to apply broad swaths of color. The artist
might also apply paint with a palette knife, which is a flat,
metal blade. A palette knife may also be used to remove paint
from the canvas when necessary. Some artists even paint with
their fingers.
Most artists paint in layers. The first coat or "underpainting"
is laid down first, painted normally with turpentine thinned
paint. This layer helps to "tone" the canvas, and
cover the white of the gesso. Many artists use this layer
to sketch out the composition. After this layer dries, one
way the artist might then begin is by painting a "mozaic"
of color swatches, working from darkest to lightest. The borders
of the colors are blended together when the "mozaic"
is completed. This layer is then left to dry before applying
details. After it is dry, the artist will apply "glazes"
to the painting, sometimes using a process of "Fat over
Lean" which means more oil/paint ratio than the previous
layer. A classical work might take weeks or even months to
layer the paint properly. Artists in later periods such as
the impressionist era often blended the wet paint on the canvas
without following this layering method. This method is called
"Alla Prima." When the image is finished and dried
for up to a year, an artist would seal the work with a layer
of varnish typically made from damar gum crystals dissolved
in turpentine.
