Since ballast materials are generally used for their density only, the technical specification is not too important, but price is. The market is split between metallic ferrous, and non metallic. Due to the corrosion problems with metallic ballast , particularly due to expansion of the ballast material when it is wet many customers are using non metallic ballast. Metallic ballast is usually iron based, Washot is Wolverhampton Abrasives proprietry brand. Chilled iron and steel media are also available from Wolverhampton Abrasives range of media. Washot is a very cost effective material compared to traditional ballast materials. The non metallic ballasts, start with the cheap iron silicates which have approx. 50 % bonded iron; but the density is not as high as metallic materials. A half way house between iron silicate and Washot is ferro silicon which has a higher iron content than Iron Silicate