Mediums & Varnishes
There is an overwhelming collection of little bottles filled with additives and fixatives available to change the behavior of your paints. Each will allow you to vary your paint in the most subtle or dramatic ways based on the substance. While you may be tempted to buy everything available, start with some basics and build your stock from there carefully. Learn to read and understand labels, and find out what your favorite artists use and duplicate their efforts.
Mediums
Mediums are mixed with oil and acrylic paints to enhance the pigments’ behavior
usually through manipulating flow. Separate mediums are used for oil-based
paints and water-based paints.
For Oil Paint
Mediums for oil paints are made from mixtures of separate products
with which an artist plays (often in capped bottles as shown below)
to develop his/her own recipe. For example, a traditional medium
mixture is one part Damar varnish, one part stand oil, five parts
turpentine and a few drops cobalt or Japan drier. Mediums may also
be bought in pre-made mixtures. Commercially made mediums can vary
as much as home-spun recipes. Whether homemade or store-bought, mediums
can be placed in a lidded glass jar and reused for many painting sessions.
For Acrylics
Although acrylics can be thinned with water, they lose quality in the
process. Mediums can aid in the flow of acrylics without changing
the hue or intensity of the color. In fact, acrylics can be heavily
manipulated with the bevy of new mediums now on the market. Gels
will thicken acrylics for an impasto effect, retarders slow drying
time, and tinting mediums alter hue and/or color intensity.
For Watercolors
Generally, watercolors are mixed with water for creating transparencies,
but mediums such as Gum of Arabic or even acrylic mediums can increase
the brilliance of colors. There are also several different mediums
available to increase the fluidity and texture
of watercolors.
Mediums
As you experiment with mediums, keep in mind these guidelines:
1) Use the minimum amount of medium to serve a particular purpose. Conservators seem to be in agreement that oil paintings done with straight paint (no mediums except a little thinner) form the strongest, most permanent films.
2) When using gobs of oil-containing gel mediums to build up texture, there is significant danger of yellowing.
3) Yellowing is sometimes rapid and pronounced when a painting is left in darkness; the yellowing will gradually lighten as the painting is exposed to normal daylight.
4) Mediums containing copal varnish are likely to darken significantly.
Varnishes
Varnishes are solutions of natural or synthetic resins in solvents. For
example, damar varnish is damar resin in turpentine. Shellac varnish
is a solution of refined shellac in alcohol and wax varnish is beeswax
in turpentine. When applied, the solvent evaporates and the resin dries
to a solid transparent film. Varnishes can be used in a number of different
ways with specific varnishes made to meet each requirement.
Picture Varnish
This varnish is layered over a finished painting to coat and protect
it from dirt, dust and atmospheric impurities. It dries colorless
and transparent, can be glossy or matte and some are removable.
Retouch Varnish
This is a heavily thinned varnish with a lot of solvent and less resin.
Oil paintings are often produced in layers with new layers applied
on top of dried ones. When the paint dries, it tends to look more matte,
in which case the paint added, even if it is the same hue or color,
looks different even though it is not. This issue can be bothersome
and can often hinder one’s color judgment. Retouch varnish is
applied in thin layers in order to achieve the original wet-look when
painting is resumed.
Mixing Varnish
Varnish, most often damar, is regularly combined with mediums to thin
oil paints before they are applied to canvas. In small amounts, it
can make oils thinner, more manageable and more glossy. In large amounts,
it can thin oils down to a glaze. Although it is possible to mix varnish
alone with tubed paints, it is rarely done.
Varnishes
1) If you are new to varnishing, practice first on a test painting.
2) Glossy and matte varnishes are both available, and may be used independently or mixed to achieve the level of finish you desire.
3) Use a clean varnish brush two or three inches wide to reduce the chances of brush overlay marks. Try to cover in one or two long strokes, and avoid fussing with the varnish as it begins to set.
4) If you are using spray varnish, lean the painting at an angle against a wall and hold the spray nozzle at least twelve inches away. Keep the nozzle moving, and let each film dry before applying the next. Don‘t try to varnish too fast or the excess will end up running down your painting.
5) Always varnish a dry surface in a dry, dust-free environment. The slightest moisture will cause bloom–an unsightly whitish mess.