Issues of contemporary patination on outdoor bronze sculpture

Joanna Rowntree


This talk will address some examples of patination pitfalls in the conservation of outdoor bronze. Artists demand a wide palette of colors on the surface of bronze sculpture. Some of the colors desired are not available using patina chemicals alone. Chemical patinas can be augmented using pigments, tinted coatings and/or paint. Sometimes even more traditional colors are mimicked through the use of these techniques, especially if a successful chemical patina cannot be achieved quickly or effectively. These types of surface colorations tend to be less stable over time, and the color can be potentially fugitive. Additionally, sculpture sometimes has a metal finish on the surface which can be difficult to patinate. If the surface is sanded to a fine grit level, this compacts the bronze, preventing good color adhesion. Dense, black patinas can pop off the surface within months of application. This level of sanding is done on smooth surfaces, not textured ones. On a smooth flat back surface, any attempt to spot patinate the bare spots can lead to visible irregularities in the surface coloration. Finally, one traditional patina chemical can discolor significantly when applied to silicon bronze. There is an unpredictable reaction that occurs when cupric nitrate is applied hot to the surface of silicon bronze. The normal, dense green turns red and blotchy. These areas of discoloration darken over time and can lead to a misinterpretation of the intended color. The sculpture can appear to have been dark brownish red intentionally with a green corrosion layer on top. In order to avoid this color shift, the traditional hot cupric nitrate patina has been replaced in some instances with a cold green chemical. The cold green chemical formulas are trickier to apply, less stable over time and shift dramatically in color if hot waxed. As conservators, it is important to have good communication with the fabricator or foundry. It is also important to have a basic working knowledge of patina chemicals and what they tend to look like in order to identify some of these situations.

2002 | Miami | Volume 9