Cleaning an oil painting - Varnish removal.

The illustration left shows the effect of varnish
and surface dirt removal. (See also Paint Structure).

This process involves special solvents and chemicals
which inhibit the solvent action. The use of these
solvents requires great precaution, knowledge and
skill as often the same chemicals will also dissolve
the paint binder. Preliminary tests are made to
establish which solvents are appropriate to each
painting technique.

Most paintings of any age will develop cracks as the
pigment and binding agent contract at different rates
to the canvas and primer. These cracks will harbour
surface dirt and discoloured varnish (resin varnishes
change colour over time and become amber-yellow)
and as with impasto pigment areas, are treated with
dental tools or a scalpel.

"Cupping" of these islands of pigment is an indication
that the painting layers have become loosened from
the canvas and may require "re-lining".

Re-lining an oil painting.

The illustration left shows the removal of the "facing"
tissue which is applied to the surface of and oil
painting to protect it and to temporarily hold any
loose pigment areas or canvas tears in place.

The painting is first taken off its stretcher, faced, then
laid down onto the lining table. A heat sensitive glue
is then pasted onto the old canvas and a new canvas
is laid onto the old, suspended on its own stretcher
or loom.

When heat is applied to the new canvas, the "glue"
passes through the canvas layers into the primer
and finally into the pigment layers securing the entire
structure.

The materials used have been developed specifically
for this purpose and are well tested for longevity.
Most oil paintings of any age have at some time
been lined. As techniques have progressed old linings
must sometimes be replaced with new.