Patina and the Watchful Eye: A Dialogue with David Phillips

David Phillips's watchful approach to the aging and alteration of his outdoor bronze patinas presents conservator Rika Smith McNally with the opportunity to listen, look, and respond to this artist’s thoughts regarding the subtleties of color and surface as they affect the maintenance of his bronze sculptures.

For this exhibition, David has loaned CAC the two cast silicon bronze fragments you see here to serve as conversation pieces and samples of applied patinas. These two bronze fragments are from Water Strider, a temporary installation David completed in 1991 in the outdoor fountain at the Christian Science Center in Boston. After the exhibit was dismantled, the fragments were stored outdoors at David’s studio, and, more recently indoors. The original patinas have altered over time.

Rika Smith McNally:
Comments on the care of David Phillips’s bronze artworks

“I have known David Phillips's public artwork for many years, including the several outdoor bronze and granite examples in the collection of the Cambridge Arts Council [see exhibit map].

David prefers his bronze patinas to be exposed to the weather and change over time, but he does not want them to age or alter to the point of looking deteriorated or uncared for. At CAC, our conservation goals for David’s sculptures are to watch them carefully--and then decelerate aging when an artwork gets to a stage the artist likes. We monitor his sculptures in the collection every year, photographing their slow alterations and giving them a gentle washing and protective wax coating.



David is very much a part of this process. As a conservator, I understood from our first conversation years ago not to automatically assume that change to a patina was undesirable. Some of David's outdoor artworks in other parts of the world have received no maintenance. The patinas have been left to change in their environment, and have deteriorated beyond the state he intended. In Cambridge, we are trying to avoid that.”

David Phillips:
Observations on silicon bronze

“I have used silicon bronze in my sculpture for the past 25 years and also at the Massachusetts College of Art, where I teach a foundry course. Silicon bronze is the alloy of choice for many art foundries. It has excellent welding characteristics - the welds don't show through patinas as they do in other alloys. It is considered a marine bronze, making it excellent for outdoor sculpture. Also there is no lead in this alloy, so it is relatively safe during melting and grinding.”

Sample patinas

A conservator is trained to research the history and original fabrication of an object and establish conservation criteria to arrive at logical treatment proposals. Rika’s first step in patina experimentation on the two fragments displayed in this exhibition was to examine photographs of two versions of Water Strider--the 1991 temporary installation in Boston as well as a permanent Water Strider fountain located at Eastern Connecticut State University (1992). Pictures of the Boston version reveal that the original green patina was evenly applied across the surface. Photos of the Connecticut piece, in contrast, show a more mottled surface, with the blue-green patina color closely matching the appearance of the small juniper bushes David had planted within the structure of the bronze.

Rika and David agreed to the following options for the sample patinas:

Is one treatment better than the other?

Rika: “The wax treatment is a more cautious treatment, because it would be easy to entirely remove it with an organic solvent (a petroleum distillate). It would also be easier to repair a small area if was damaged. I felt a little more comfortable with this treatment, because I had continuous control over the color and application and I could slowly build it up. The more blue-green patina in the second treatment, however, reminded me of other patinas I have seen in David's work, so I was interested to hear his thoughts.”

David: “I feel the waxed patina, even though it has more depth, richness, is a bit too precious for my fountain. This is not the kind of patina I would ordinarily put on an outdoor bronze. The cold green patina is closest to the matte color I prefer."

When the Material Choice exhibit is over the bronze fragments will be melted down at David's foundry in Medford, Massachusetts, and used to cast new sculpture.

David: “It has been great working with the Cambridge Arts Council and with Rika on this project. More than any of the other states and art councils where I have installations, the Cambridge Arts Council has been most conscientious in preserving their public art collection.”

What is the difference between silicon bronze and statuary bronze?

Silicon bronze is an alloy of copper, silicon, and manganese. The most common alloy used by art foundries today is Type A bronze, known as Everdur, and is 95% copper, 4% silicon, and 1% manganese. Historic bronze, commonly referred to as statuary bronze, is typically an alloy of 90% copper and 10% tin.

Silicon bronze is more resistant to corrosion than historic statuary bronze, but it is more difficult to patinate, as some of the more traditional applied patinas don’t react as quickly to the Everdur (the property that makes the bronze more resistant to corrosion also makes it more resistant to applied patinas).

In some cases, a patina chemical that produces one color on historical bronze will result in a very different color on silicon bronze. For example, cupric nitrate, a common chemical reagent used to create a green color on traditional bronze, can turn dark reddish brown on silicon bronze, and they can change differently than traditional bronze over time (staring with a shift to a darker tonality after fabrication instead of the light green copper sulfate corrosion product expected on older bronzes).

Modern foundry patinators have learned to use different chemicals or techniques on silicon bronze than historic bronze, and may also add pigments such titanium oxide or chemicals such as bismuth nitrate for certain effects.

The importance of communication

Conservators can gain significant knowledge from continued conversations with contemporary sculptors and modern patina masters. It is essential for artists, foundries, arts agencies and owners to keep careful records and share knowledge of an artist’s work.

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