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Some Improvements in Zoological Microtechnique for Electron Microscopy

Preparation of Glass Knives

Preparation of Glass Knives

Several books mention the use of "float", "drawn" or Libbey-Owen plate glass for the making of high quality knives. This glass gets its name from a process whereby freshly-rolled plate glass is passed over the surface of molten lead before cooling. The idea behind this is to anneal the surface of the glass to relieve the strain formed during cooling. We wondered if it was better to subject the glass to a treatment which would give a more deep-seated release of strain, since less strain in the body of the glass seemed to us more important than a stress-free surface.

Glass and toffee share few similarities, but there is one which in our opinion seemed most important. Both these substances are essentially amorphous solids that on heating melt to form viscous liquids and on cooling again become solid without crystallisation. If one wants to crack toffee easily and cleanly, it should be cooled in a refrigerator. We applied the same idea to the glass plates from which the knives are made, and found that much better knives could be made from cold glass than from glass held at room temperature. So we now keep all glass to be used for knives in a refrigerator at a temperature of −5°C.

Some books recommend that slow fracture of glass produces better knives; but a slow fracture is not easy to achieve. It can be accomplished much more readily if the glass is cold when placed under strain in the knife-maker and page 3 allowed to stand. A slow rise in temperature allows the glass to expand and thus apply the final strain to induce slow fracture. Using this method, we can make first-class knives from plate-glass sold by glass merchants.

In our opinion the edge of a knife made from cold glass lasts longer than one made from glass held at room temperature, and shows evidence of being sharper. The making of the knives is much simpler and easier and there are virtually no rejects because the glass fractures so cleanly. Consequently, there is a great saving not only in time but also in glass. We use a Japanese Messer knife-maker. Each knife is washed in absolute alcohol and then 100% acetone to remove water of condensation.