 As the ash percentage decreases, the artist has more control on the color and the final glaze color, using wood, differs from light to dark shades of brown or green, if no other coloring agents are added.Rice-straw ash glaze produces an opaque creamy-white glaze; it is high in silica.If the ash is very thick, there may be sufficient phosphorus to give an "opalescent blue"; rice-husk ash is good for this.