 Picture
frames have traditionally been made of wood, which
is still the commonest and most prestigious material,
although other materials are also used, including
aluminum, plastics or polystyrene, even sea shells.
A picture frame may be of any colour or texture, but
gilding is common, especially on older frames. Some
picture frames have elaborate mouldings which may
relate to the subject matter. Complicated older frames
are often made of moulded and gilded plaster over
a plain wood base.
The picture frame may contain a
pane of glass or a plastic glass substitute such as
Plexiglas, in order to protect the picture. In some
instances where the art in the frame is dispensable
or durable, no protection may be necessary. Glass
is common over watercolours, rare over oil paintings,
except very valuable ones in some museums. Glass may
be treated with coatings, the most common being UV
filters. Some glazings such as Denglas, Optium, and
Museum glass have a coating which makes the glass
partially nonreflective and practically invisible
under ideal lighting conditions.
The elaborate decoration on this
frame may well be applied plaster pieces stuck to
the wood beneath
For pieces
to be framed under glass, except for the most disposable
and inexpensive posters or temporary displays, the
glass must be raised off the surface of the paper.
This is done by means of matting, a lining of plastic
"spacers", shadowboxing, stacking two mouldings
with the glass in between, and various other methods.
If the paper (or other media) were to touch the glass
directly, any condensation inside the glass would
absorb directly into the art, having no room to evaporate.
This is harmful to almost any medium. It causes art
sticking to the glass, mildew, and other ill effects.
Raising the glass is also necessary when a piece is
done in a loose media such as charcoal or pastel,
to prevent smudging. Care should be taken with these
works, however, if Plexiglas is used as a static charge
can build up which will attract the pigment particles
off the paper. Using real glass helps to prevent this.
Certain kinds of pieces do not usually
need glass when framed, including paintings done in
acrylic or oil paint (the former is usually waterproof;
the latter actually needs to "breathe" due to the
decades-long drying process), stained glass or tiles,
and laminated posters. These kinds of pieces are still
sometimes put under glass though if for example, they
are framed using mats, or (in the case of oil paintings)
they are kept in a carefully climate-controlled environment.
Certain kinds of pieces do not usually
need glass when framed, including paintings done in
acrylic or oil paint (the former is usually waterproof;
the latter actually needs to "breathe" due to the
decades-long drying process), stained glass or tiles,
and laminated posters. These kinds of pieces are still
sometimes put under glass though if for example, they
are framed using mats, or (in the case of oil paintings)
they are kept in a carefully climate-controlled environment.
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