The vermiculite containment form turned out fine. The plaster/silica investment core turned out fine as well. After several tries I was able to stack the cut-glass strips snugly between the core and box walls. (I forgot to photograph this process.) From this point on, everything that could have gone wrong did go wrong due to bad judgement calls. The glass stuck to the vermiculite form, the glass cracked, and the mess you see below is the result. Do I understand enough at this point to try it again and is it worth it? I haven't decided yet.