Producing Improved Glass Knives for Ultra-Microtomy; A Glass Breaker Featuring a Linear Fulcrum and a Device for Controlling Fracturing Velocity

Innovations include: (1) interchangeable round linear fulcra of different diameters, (2) compressible materials covering pressure sites, and (3) a screw-compression mechanism for initiating breaks and controlling fracturing velocity. The instrument consists of a cross-shaped pressure plate hinged to a rectangular metal base bearing the pressure-applying mechanism opposite the hinge. A longitudinal slot in the pressure plate parallels the long axis of the fulcrum and permits positioning of prescored glass pieces or permits scoring of an engaged glass piece by guiding a scorer inserted through the slot. Knives with straight, flawless edges have been obtained from different types of glass (up to 7/16 inch thick) including soft, pyrex and tempered. Greater than 50% yield of useable knives averaging more than 50% of flawless edge, as judged at a magnification of 220 and by ultrathin sectioning, has been obtained with the device. The instrument design and technique facilitate controllably reducing the fracturing velocity to significantly increase the width of stress-free knife edge obtained. Details of the technique, optional attachments and modifications are outlined.