There are several things that can contribute to a lack of shininess. A too-thin layer of glaze won't have enough thickness to become shiny and reflective. If poured when still too hot, much of the glaze can run off and result in a layer with not enough glaze, or it could melt or soak into the layer beneath. Be sure to pour when the glaze reaches an appropriate temperature and try to ensure the glaze forms a substantial layer.