Process Overview
The first step of this process is to make a virtual 3D model. And from that, a model of a single-part mold, with an opening at the top through which concrete can be poured, and a stable base that keeps the top level. That form is then 3D printed using an FDM-type printer, and PLA plastic (note: avoid PLA plastic with additives such as PHA, which can inhibit the concrete from setting). The next step is to create a concrete mixture including water, alumina cement, aggregates such as grog and molochite, flux, clay, and various additives for strength and flow properties. That mixture is then poured into the form, and some means of vibration is used to get bubbles out (we use a handheld massager from a thrift store, or a more powerful table-mounted concrete vibrator). Then the top is covered to inhibit drying while the cement sets, and the form is left for at least 24 hours before uncovering (though longer is better). The cast is then dried by candling in a kiln overnight under 200°F. Next we melt the plastic at between 400°F and 430°F and either remove the plastic from the kiln before proceeding, or simply raise the temperature further to burn the plastic off. At this point the form is brought either to bisque, or to its maturity temperature. And next the form can be glazed and fired again.
