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.
145 George Street, The Rocks group as a whole, contributes to a precinct unique to NSW with its historic associations and streetscape character. The group is an important part of The Rocks Heritage Conservation Area being sympathetic in scale and character and an extension of the remaining earlier buildings of George St, presenting a unified streetscape. The buildings are tangible evidence of the redevelopment of The Rocks in the last decade of the 19th century and first decade of the 20th century. 145 George Street has high social significance as a contributory element associated with the historic character of The Rocks, which is held in