A diamond knife is a very sharp knife whose blade is made from diamond. The cost is very high; diamond knives are used for scientific applications where an extremely sharp and long-lasting edge is essential.
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When the development of ultramicrotomy evolved, it was also determined that metal knives made of standard histology or razor blades were too dull to cut ultrathin sections. The metal knives were soft and fragile and would lose their cutting edges when thin sections were required for transmission electron microscopy. In 1959, Latta and Hartman discovered that the edge of broken glass could be used to cut thin sections of specimen. Glass knives are very popular in ultramicrotomy for trimming specimen blocks and cutting thin sections. However, some hard specimens, such as bone, plants, and thick-walled spores, are difficult to cut, even with a good glass knife, because the edge dulls too quickly.[1] Humberto Fernández-Morán discovered that a gem-quality diamond could be used to fabricate a more durable knife for use in the microtomy process; diamond was a logical material to use since it is the hardest known material.
Diamond knives are both delicate and expensive, usually costing several thousand dollars. Natural gemstones used to produce diamond knives are usually pale yellow, of regular crystal structure and of the greatest possible purity. Diamond dust is used on a turning table to cleave large stones into smaller segments. The grinding process usually reduces the stones to 50% of their original weight. The diamond blade is then mounted into a soft metal shaft (Wood's metal) and finally polished to a very sharp edge. The knife's edge is extremely sharp and free of imperfections, which helps to get accurate views of specimens at high magnifications with the transmission electron microscope (TEM).[2] The shaft containing the final edge is then mounted in a metal trough, or "boat", and cemented, usually with an epoxy plastic.
There are many styles and types of diamond knives. For the most part, they can be made for use dry or wet. Blade angles of diamond knives vary from 35 to 60 degrees. The smaller angles knives are used for finer cutting, but these knives are prone to damage. Wide angle knives have better life expectancy.