The pour on August 26 went smoothly. We followed several suggestions offered both by Colonial Williamsburg tradespeople and experienced founders from outside the Foundation. Before the pour, the mold was fired in a modern pottery kiln at the College of William and Mary (Brad, thank you!) to approximately 1500-1550 degrees Fahrenheit. This resulted in a much more “ceramic-like” material, with all the fiber and any remaining wax burnt out of it. That eliminated several variables. We eliminated two others by using a modern flux and degasser. When the furnace was tapped, the flow of bronze appeared to be less viscous than that of our first attempt, and the material itself was a bright, gold color. A bit of the initial flow was diverted from the mold cavity.
The mold filled nicely, and the observed shrinkage looked good. The next day, Thursday afternoon, we excavated the mold and broke it away to reveal a smooth-surface casting with nice detail. On Friday afternoon, we sawed off the deadhead. While the surface revealed was a vast improvement over the first casting, it still had a ring of small (pin-head size) holes just below the surface and some small shrinkage gaps. Slicing the deadhead a couple of inches above the first cut revealed more porosity.
Although we won’t know until we clean the surface of the mortar-portion of the casting, our hope is that the defects diminish toward the bottom of the casting. If so, we may have a mortar. We’ll find out over the next couple of weeks and let you know.
Once we are satisfied with these experimental castings, we will begin “reverse-engineering” the modern technologies we are using in an effort to complete the entire process using only period methods.