A New Method of Glass Knife Preparation for Thin-Section Microtomy

An approximately 3 ram. wide strip of thin adhesive plaster is attached to one jaw of a pair of standard, fiat glass pliers in a manner shown in Fig. 1. The marked line is placed on the side opposite to the strip (Fig. 2) and the pliers closed over it with a steadily progressing pressure. The thickness of the adhesive acts as a wedge against the glass mark and effects a slow and clean break. The thickness of the adhesive tape is determined by the type of glass used and the thinnest effective adhesive should be selected. For 1/~,, "crystallex" plate glass (Pittsburgh Glass Co.), a single layer of plastic stripping is adequate. An increase in the thickness of the tape or the addition of two further strips to the opposite jaw of the pliers, forming a distinct 3-point pressure, would appear to make the breaking easier but this increases the stress at the moment of breakage, resulting in minute fractures at the edge of the knife similar to those caused when a knife is accidentally dropped onto a hard surface. The pliers are equally effective in line-breaking, that is, along a line scored right across the whole plate as in strip cutting, as well as in stressbreaking (where only a short starting mark is made at the edge of the plate and the glass is allowed to break along its inherent stress lines).