When working with rare-earth colorants, use titanium dioxide. Using rutile will cause the glaze to over-crystallize. Mix to a specific gravity of 1.45 and apply by dipping a piece into the glaze for 3 seconds. This glaze crazes on some porcelain bodies, and goes matte on some stoneware bodies. I use Coleman Porcelain from Aardvark. If applied too thickly on Coleman Porcelain, the glaze can craze slightly. Fires to a glossy surface at the right peak temperature, but a slightly lower peak temperature and lead to more matte surface.