Yes you can use oil on the glass, but stretch one or two layers of plastic wrap over the plate first, before applying you mix. Wendy

I make birdbaths with large platter type dishes imbedded in the mix. The dish can be an attractive color, and it will be watertight. The BB could be molded with the dish removable, but mine are always perminently in place. Dishes can be bought at a dollar store or a cut-rate pottery place.