Plastic Deformation of Glass during Scratching

RECENTLY a short note by E. W. Taylor on plastic deformation of optical glass1 has appeared. In this connexion a photomicrograph of scratches made on an ordinary microscope slide glass by a diamond is shown in Fig. 1. The diamond was shaped in the form of a cube with its faces parallel to cube planes and one cube corner was used as the scratching point, so that a body diagonal of the cube was perpendicular to the glass slide during scratching. In this position a (110) plane of the cube is also perpendicular to the slide, and the direction of scratching lies in this plane. The scratches, as reproduced, were made with an edge of the cube leading (the other possibility being that a face is leading). The angle between the cube edge and the plane of the glass slide was about 35° (ideal value 35° 16′).