In 2008, in an effort to create re-usable molds I took a class at Polytek in Easton, PA. They manufacture rubbesr, plastic, and all manner of mold-making and casting materials. This vase was the earliest result. It consists of a concrete block inserted into a Crate & Barrel-bought 4"x4"x14" glass vase. This block is designed to have corners and sections cut out of it. I then drilled through it lengthwise in three locations, and inserted fiberglass wicks down the length of those penetrations. The vase, with the concrete block inside it was then filled with lamp oil.
In dim light, the polished top edge of the vase catches the light and refracts it back into the vase, illuminating the faces of the concrete block for an interesting effect.
This is a pic of the rubber mold and both rubber and plastic casts.