Bronze Restoration: The Deterioration Process and Useful General Care Guidelines

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...