Extending the Life and Use of Glass Knives

Not everyone can afford to use diamond knives on a routine basis. There are occasions when the use of glass knives is a wise option. Specimens processed outside the laboratory may have unexpected hard inclusions so preliminary cutting with a glass knife will determine if it is safe to proceed with a diamond. Rough cutting into the specimen to reach the required level before using a diamond is also a wise use of glass knives. They can also be a valid alternative to diamond for cryo sectioning. Making the most of your glass knives. TAAB glass (G067) specifically selected for the making of glass knives is available in 6mm, 6.5mm and 10mm thicknesses and the following procedures apply to all sizes. Wash the glass before use with a dilute detergent and rinse well with distilled water. Dry with a lint free cloth. Always make the break as slowly as possible (faster breaks create more stress resulting in a less even edge). Although the most usable edge is just above the left of the main stress or Wallner line there is some evidence to show that the edge to the right is still useable for some applications and possibly sharper and longer lasting. The stress release in the glass is very fast but short lived, so knives can be made in advance and, if kept clean, can be stored for months (H. Sitte: Ultramicrotomy - Common Problems and Mistakes). The story goes that early electron microscopists were often seen combing the Glasgow scrap yards searching for the plate glass windows of recently decommissioned trams in the belief that the seasoned glass was better for making knives! Whether this was true or not they certainly became skilled at making knives by hand. The luxury of commercial mechanical knife breakers did not appear until 1962. Making Floatation Baths. Boats can be preformed as in the Leica/LKB Truf and sealed to the back of the knife with wax (W050) or varnish (S343). These have the benefit of providing a larger surface area for sections. You can use silver tape (T066) if you need some bling. We recommend SLEEK medical tape (T366) which can be attached rapidly and pressed into position to make a water-tight seal without wax or varnish (ask for TAAB data sheet "Making an ultramicrotome boat with SLEEK Tape). If you need a larger water bath use SLEEK tape on a 10mm knife for these occasions. Improvements can be made to knife performance (whether for ambient or cryo sectioning) by the evaporation of a tungsten (W067) layer onto the knife back and front surface (Roberts 1975 and Griffiths et al 1984). This lengthens knife life and permits sectioning of harder materials – for reasons unknown! Visit our web site today (www.taab.co.uk) to see the full range of sectioning accessories, diamond knives, and all things microscopical.