For
imparting the smart look to their wooden furniture most people prefer varnish
rather than any other wood paints. There are several other applications for
varnish apart from improving the aesthetic quality of furniture or doors. There
are many other uses for it. Two basic types of varnish exist: spirit and
oleo-resinous. The spirit varnish that is most useful is shellac varnish i.e.
shellac dissolved in alcohol. These forms of early varnishes are based on
resins that come from natural sources. At present, certain varnishes come from
synthetic resins also.
Resin
dissolved in turpentine together with a drying oil like linseed oil is known as
varnish. The varnish may be made of many different types of resin that are available
and the resin is selected according to its application.
There
is little or no colour in varnish and it is transparent. When it is applied a
hard, protective layer of film is formed on the surface. Extensive use of this
surface finishing product is made on wooden surfaces ranging from doors to
furniture. Usually varnishes are glossy but may be designed to produce
semi-gloss sheens by adding certain chemicals known as flatting agents.
When
a picture is painted, a final coat of varnish is applied to protect the
picture. This makes the surface appear uniform. The surface appears either
matte or shiny or the paint film is protected from chemical reactions to the
atmosphere. Mixing varnish is an additive to normal paint. It is utilised as an
additive to the painting medium and reduces the drying time and gives a glossy
look.
Turpentine
is a thinner for paint and there are other mineral spirits with the same
properties. Both could be harmful to the painted surface. A variety of varnish
known as isolating varnish is a resin that does not dissolve in mineral
spirits. When it is applied to paint film, it will safeguard it from being
affected by turpentine and mineral spirits in the underlying paint layer.
There
are many different types of varnishes that have different uses:
Shellac:
Shellac
is a resin that is taken from the lac insect. It has a tendency to crack and
darken on paintings with age. It is insoluble in turpentine but dissolves in
alcohol. After drying, it becomes hard, tough flexible film whenever applied to
anything besides the surface of a painting.
Dammar Varnish:
Dammar
Varnish is more popular than any other varnish and is used to either retouch,
mix or as a Picture Varnish. It does not put on a chalky appearance and is not
as yellow as most natural resins.
Copal Varnish:
Copal
Varnish is comparatively less used and has been replaced by synthetics as
alkyds or unnamed tree root resins. If used in moderation, it makes a very good
isolating varnish and a very hard surface final varnish. With age, it darkens
and cracks. It often needs no drying agent.
Mastic Varnish:
Mastic
Varnish is clearer than Dammar and is easier to apply. In humid climates, it
may develop a chalky appearance. It is more yellow than Dammar and is far more
costly. It is rarely used as a Picture Varnish but usually as a Mixing Varnish.
Synthetic Varnish:
Synthetic
Varnishes are usually made up of acrylic resins dissolved in mineral spirits.
These, dry soon, are clear as Crystal and are not as yellow as most natural
resins. Unfortunately, they can be used only as Picture Varnish.
Polycyclohexanone has developed recently and is an exception. It is less yellow
than Dammar.
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