I was wondering that the zinc might be fluxing something when I first saw it, but I to quickly assumed the structures coming out of the trays were testing probes or something put in after the firing. Now, my guess would be that you are growing crystals. I would guess that the narrow tops are from the lower energy level of the early vapor condensation and accretion on I guess a crystal imperfection, then when the material became more energetic the diameter expanded to allow the molecules to order themselves accordingly. The structure has to be light enough to be lifted by the surface tension of the source material. But, that is a very uneducated guess. Beyond that, wow, how cool!