This week's blog is written by Carl Sandeen of Kristi Usher Fine Art. Carl's wife, Kristi, is a bronze sculptor of western themes as well as a two-dimensional artist with oil, pencil and ink. Kristi's work is known for realism and projects her intimate knowledge of horses, dogs and the cowboy way of life.
Bronze patina is a thin layer that forms naturally on the surface of the metal alloy by oxidation over time. This oxidation is quickly evident in sculptures installed outside such as the larger than life-sized bronze of Chief Joseph seen as you drive into the town of Joseph, Oregon. However, patina, especially for smaller pieces that will remain indoors, is produced by chemicals introduced in the last part of the production process.
There are many steps to producing a bronze
sculpture. Besides sculpting the object in, most commonly, an oil-based clay, there is the cutting up of that initial sculpture into pieces that can be cast. These pieces are carefully molded with rubber and strengthened with plaster. Then wax is poured
into each of these molds. The wax positives are removed and covered with ceramic material that will be cured in a kiln as the wax melts out. The ceramic molds, reflecting each of the saved rubber molds, are now filled with molten metal then broken away when the bronze solidifies. The pieces are fitted, welded, and finished to resemble as closely as possible the original sculpture created by the sculptor.
It is time for the patina artist to do his or her work. The patina artist is a seasoned combination of foundry worker, chemist, and most importantly artist. In this final step it is artist collaborating with artist to produce a piece of fine art that will inspire and best represent the vision of the sculptor.
A typical chemical formula that will produce, for example light transparent green, includes sodium thiosulphate, ferric nitrate and distilled water. Skillfully applied by brush, and torched with just the right amount of heat, permanent color will be etched into the bronze metal surface through controlled oxidation.
Color after color, from chemical formula after chemical formula, the palette of the patina artist will bring a piece of fine art to its desired beauty.
Kristi can opt for a traditional patina that is brown with some bronze highlights showing through. But most often her bronzes are "full color" with bronze highlights, though she likes to keep the colors subtle.
Before the finished bronze leaves the foundry, it is buffed with carnauba wax and mounted to a base that
complements the sculpture. It is now, after many hours or work, finally ready for gallery display, purchase and finding a new home.