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.
95-99 George Street, The Rocks buildings form an integral part of what was the major commercial centre of the colony, which has continued in the same use to the present day. As a group, the shops along the western side of George street have a landmark streetscape value, providing a strong architectural statement on the major entry into The Rocks. While differing in style, the buildings are sympathetic in materials and scale and form a unified visual precinct, and make a major contribution to the significance of The Rocks Conservation Area. The sites have strong associations with former uses and owners including the early penal