Bronze restoration and conservation is
both a science and an art.
Understanding the environmental conditions an outdoor artwork is exposed
to is like checking the weather before going out on a blustery winter’s
morning. We research the conditions, prepare and plan, and then execute
effectively; or we pay the price in some way. While bronze sculptures are
certainly more resilient than our human bodies, they are exposed 24 hours a
day, 365 days a year to constantly changing conditions. The transient nature of
weather is just as damaging as the severity of its extremes. Consider this as you
delve deeper into the preservation and conservation of the outdoor art for
which you may be responsible.
1.
Environmental causes of corrosion, degradation and deterioration
Outdoor bronze sculptures face the
additional complexity of harsh elements and their combinations. Humidity,
temperature, ultra-violet light, proximity to fresh or salt water and air
pollution all combine to alter the patina and degrade the metal.
In addition, the sulfides or sulfuric acid in "acid rain” are extremely harmful, causing streaking and other visible blemishes on the surface.
2. Time frame for restoration process
An outdoor bronze may well have spent
decades without any conservation treatment. In most cases, the original patina
will be difficult to uncover; thereby requiring research about artist, casting
location and other references to its initial patina. If research is successful,
one must then consider the original artistic intent; valuation by age and
condition, and, if any, aesthetic preferences.
The actual process will vary by degree
of corrosion, degradation and deterioration of the bronze surface. Dedication to the
outcome should supersede timing, unless there are mitigating circumstances. Conservation
requires patience to achieve the best results.
3. Caring for a restored bronze
sculpture
A regularly scheduled, documented review of a bronze should be carried
out annually. For outdoor artwork or
pieces near water, a semi-annual inspection is highly recommended to monitor
changes, treat and reduce surface corrosion, and possible future effects to the
patina and metal to help in the preservation of the artwork.
4. Current conservation methods for corrosion removal
Pressure
Washing
Especially useful for outdoor
sculpture. Corrosion products are water soluble and can be reduced or removed
using this technique. Varying the water pressure and nozzle configuration
provides a flexible and intricate method to remove the layers of corrosion and access
crevices and folds, and is also very effective on pitted surfaces.
CO2 Blasting
Also known as dry-ice blasting, this method
is similar to other forms of abrasives. Dry-ice is used to clean the surface
via pressurized air stream. Because the dry-ice pellets are soft, this controls
the removal of the corrosion layer, or the removal of a protective coating, to
restore or repair an existing patina. In utilizing thermal shock from the
pellets hitting the surface, heat is produced, allowing the flaking of the
substrate and removal of microscopic layers. It can be performed both outdoors
and indoors with appropriate exhaust vents but produces less waste product.
Remember, we are merely custodians of art...