Art of fine bronze casting

When a pristine door handle is viewed it may be difficult to grasp just how much time and skill is devoted to cleaning and fine tuning the details of the casting before it is patinaed. This process takes hours and sometimes days and some of the steps are shown below.

In the lost wax method of casting wax replicas are “gated” and wax runners or rods are attached to the wax patterns at various points so that the molten bronze can flow through these connections and pass through the gates and  fill the cavity of the shelled piece. Once cast, the runners that connect the individual castings are cut and the bronze can be recycled but a small gate end is left, and this is removed using a cut-off wheel on a hand held grinder.

The casting may contain tiny silica fragments  that were left after the wax piece was shelled that need to be removed. A handheld metal burnisher with a flap wheel made of scotch brite and sand paper is used to remove shell fragments as well as scratches, blemishes and bubbles buried beneath the surface of the casting. When bronze is poured tiny pockets of air underneath the surface are  sometimes created and are only seen once the casting is buffed when they show themselves as tiny dimples or voids. To fill the void a silicon bronze rod is melted with a TIG welder and drops of melted rod fill these voids.

Below left a grinder with coarse grade cut-off wheel. Below right a handheld burnisher with a medium coarse wheel flap and a green very coarse wheel flap.

While the burnisher is an extremely effective tool it takes a fine dremel to get into the veins and undercuts of a casting. The image here shows the tip of the dremel burr as it removes residual white shell from the leaf vein. A  dremel is an invaluable tool for fine detail and a good one will come with several burrs, rasps and files. The dremel bits are made from tungsten carbide steel and fit into the dremel socket which when rotating at a high speed can cut and grind silicon bronze and even 316 stainless steel.

A fixed buffing machine with coarse and fine scotch brite disks is used to clean remaining marks or scratches. The casting is pushed into the path of the rotating disk which removes a small amount of the surface. A consistent and even pressure needs to be applied with the buffing disk to avoid unwanted grooves and directional marks.

A simple and complicated mold for lost wax casting

  A simple and complicated mold for lost wax casting

 Martin’s art journey continues and the story line of the insect world of giant insects is evolving as he begins to depict the dung beetle’s family life.

In nature many dung beetles have been photographed  moving their prized dung balls with alacritous backward leg movement. The dung ball is prized as it can be used as a food source or as a site for the female dung beetle to lay her eggs in which is called a brood ball.

In Martin’s fictional world he has opted to create a more faceted airy dung ball and one with organic hollows that will eventually be populated with offspring or dung beetle artifacts.

The patterns has been created, 3 molds have been made and the first red wax replicas have been poured.

The dung ball pattern began with a turned round wooden ball. A hollow fiberglass shell was molded over the ball by applying successive layers of fiberglass cloth sandwiched together with resin. Once set, the fiberglass ball was cut and removed from the wooden ball leaving a hollow shell. An organic design was drawn onto the face of the shell, and using a Dremel, sections were cut out and removed. The fiberglass shell was coated with three layers of gesso which was sanded to soften the edges. The shell was sprayed with primer and work on the mold began.

While the mold was made using simple compounds the process was complicated and time consuming. Layers of liquid rubber were built up inside the perforated shell. To prevent the rubber from pouring through, the holes of the shell were filled in with pieces of modelling clay molded by hand to fit each irregular hole. The outside of the shell was then coated with coats of liquid rubber and once set the rubberized outer shell was hardened with successive applications of fiberglass cloth and resin. Prior to the mold being made the pattern was treated with a release agent to prevent the mold material from forming a permanent bond. The end result is a 2-part hollow mold that is now used to make red wax replicas of the original pattern.