Sculpture From Clay to Bronze : Part 7

The patina is the color of the bronze. Patinazation is the process whereby a calculated chemical reaction between bronze, acidic chemicals, and high temperatures oxidize the surface of the metals. Certain chemicals will produce certain predictable colors when they are sprayed on the bronze and then heated. The patina process begins by heating(usually with a torch) the surface of the bronze to a temperature of 450 to 475 degrees Fahrenheit. The surface will have a nice golden appearance when it is ready. A wide variety of techniques can then be used for chemical application, the most common being done with natural bristle brushes. Chemicals can also be applied with spatter guns, spray bottles and airbrushes. The chemicals applied to the bronze will interact with the metal, creating a colored or textured appearance to the surface of the bronze. the patina has become quite an art in itself, and many beautiful combinations can be achieved. Browns, golds, and reds are typically produced through the use of Ferric Nitrate. Greens and blues can be produced with Cupric Nitrate. Whites and beige can be produced with Bismuth Nitrate and Zinc Nitrate. Silver Nitrate is very expensive, but if applied very hot and with persistence and expertise, it can create a beautiful silvery-gray patina. The ancient Asians would bury their bronzes to naturally oxidize them, sometimes for years, in order to create patinas. Today, the oxidation and coloring of bronze sculpture can take place within a matter of hours. But it is still a delicate process that should be performed with caution and with the proper equipment, preferably by a trained patineur. After the patina is applied, the patineur and the sculptor decide between two sealants to protect the patina. The traditional method of protection is to apply several thin coats of clear paste wax to the surface, which is then lightly buffed with a soft, clean, cotton cloth. This patina should last indefinitely indoors. However, if people repeatedly touch certain areas, the bronze may be expected to eventually shine through. Because today’s outdoor atmosphere is more corrosive and carries a higher content of manmade pollutants, a more durable lacquer, metal protectant  is recommended for any sculpture placed outdoors. Incralac is one such sealant designed specifically for copper and its alloys. Since Incralac produces a plastic looking, high gloss finish, the sculpture must be waxed to create the soft look of a traditional patina.     To be continued…..

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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