Scratch hardness Scratch hardness Scratch hardness tests are used to determine the hardness of a material to scratches and abrasion. The earliest test was developed by mineralogist Friedrich Mohs in 1820 (see Mohs scale). It is based on relative scratch hardness, with talc assigned a value of 1 and diamond assigned a value of 10. Mohs' scale had two limitations; it was not linear, and most modern abrasives fall between 9 and 10. Raymond R. Ridgway, a research engineer at the Norton Company, modified the Mohs scale by giving garnet a hardness of 10 and diamond a hardness of 15. Charles E.
71 Harrington Street, The Rocks Iron. As at 27 April 2001, Archaeology Assessment Condition: Partly disturbed. Assessment Basis: Area under building only. Terraced into hill slope. As at 30 March 2011, this house and site are of State heritage significance for their historical and scientific cultural values. The site and building are also of State heritage significance for their contribution to The Rocks area which is of State Heritage significance in its own right. The site has historical significance as part of the Colony's hospital site in 1807, and the building as part of the 19th century housing stock in The Rocks. It has aesthetic