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 and working classes in residence in The Rocks between the 1890s and the mid 1970s. The place is important in demonstrating aesthetic characteristics and/or a high degree of creative or technical achievement in New South Wales. The retained section of the house has aesthetic significance as part of a strong visual precinct forming a characteristic Rocks townscape with the adjacent terraces and the Harbour Rocks Hotel on the other side of the street. The retained street section of the former house enhances the human scale of the streetscape and reinforces the historic character of The Rocks. The item meets this