Iron ore
In cast iron sulfur promotes the formation of white iron. As little as 0.5% can counteract the effects of slow cooling and a high silicon content . White cast iron is more brittle, but also harder. It is generally avoided, because it is difficult to work, except in China where high sulfur cast iron, some as high as 0.57%, made with coal and coke, was used to make bells and chimes . According to , good foundry iron should have less than 0.15% sulfur. In the rest of the world a high sulfur cast iron can be used for making castings, but will make poor wrought iron.
Surface plate
Despite a fall in popularity among machine shops, cast iron remains the most popular material for surface masters (different usage from a surface plate) among laboratory metrologists, machine builders, gauge makers, and other high-accuracy industries that have a requirement for gauging flatness. Cast iron that has been properly cast is more dimensionally and geometrically stable over time than granite or ceramics, is more easily worked to a higher grade of flatness, and provides a better bearing surface to assist the creation of other master standards. These specialized surface plates are produced in sets of three, by the company that will be using them, so the plates may be regularly verified and refined without the need to send the plates out for external rework. Despite the very stable structure, cast iron remains unsuitable even in high tolerance production applications for use as a normal surface plate because of thermal expansion encountered with regular use as an inspection tool. The nature and use of a surface master, by contrast, already necessitates expensive measures to control temperature regardless of material choice, and cast iron becomes preferable.