Creating “Brock’s Bronco”
When the cladding is copper, we always use stainless steel for the armature. Copper is very reactive when in conductive contact with other metals and they quickly undergo galvanic corrosions otherwise.
The armature provides an outline for the finished sculpture. It gives a sense of location and scale in free space. It is the underlying structure that the cladding attaches to.
Here we have temporarily welded the armature to a steel plate to support it while we work.
The cladding (copper “skin”) is formed by hammering 16 oz copper sheet. Because there is ultimately a limit to how much deformation can occur in any one piece, we use many separate pieces. As the material is shaped “work hardening” occurs. The grain boundaries in the material become convoluted and must be annealed before more hammering can resume Impatience leads to holes because the material will break instead of “giving” when struck. To maintain its ductility, the copper is heated to red hot and allowed to cool (annealing). Unlike steel, it does not have to be worked hot. By annealing, the grain boundaries are relaxed making the material ductile again. This process occurs many times as each section is being formed.
We wrap the material around the armature to hold it temporarily until the next section is soldered on
This process is arduous. This sculpture is made of over a hundred individual copper sections which have all been annealed many times.
Within the spindle, bearings are mounted which ride on the main shaft (connected to the base) This provides for long lasting responsive movement.
Notice the vane arrow fletching is solid and the arrow head is hollow. In addition, the sculpture itself is set behind the spindle (toward the back), Both are critical to keep the cross sectional area “seen” by the wind on the back of the vane. This is how the vane points toward the oncoming wind.