Rutile is the mineral name for natural crystals of titanium dioxide. However in nature rutile is always contaminated by up to 15% other minerals (especially iron but also things like tantalum, niobium, chromium and tin, the analysis provided here is obviously a simplification of the real picture). The term 'rutile' is thus generally understood to refer to the brown powder into which these minerals are ground and industry accepts up to 15% contaminants and yet still calls it rutile (below 85% titanium is called ilmenite). Rutile is considered an impure form of titanium whereas ilmenite is considered as FeTiO₃. Grades of rutile are sometimes named after one of the impurities (e.g. Niobian Rutile). Rutile is used in many industries (e.g. welding rods, paint) and ceramic uses are minor in comparison (for this reason bags of rutile might have labels like "Welding Rod Titanate"). Rutile is often sourced by companies in the titania and zircon supply business. The are large reserves of rutile in the world and any supply shortages are thus related to other factors. Rutile is available in light tan calcined ceramic grade powder, darker uncalcined powder, and granular form. Either grade of powder is normally ground very fine (e.g. 325 mesh). In glazes it is generally thought to be better to use the ceramic grade (calcined) since the decomposition of raw rutile during firing could be a source of glaze imperfections like pinholing and bubbles. However in our experience the LOI (weight loss on firing) when calcining rutile is very low (less than 1%).