shape. Finally, thin sections are cut with a glass or diamond knife using an ultramicrotome and the sections are left floating on water that is held in a boat or trough. The sections are then retrieved from the water surface and mounted on a copper, nickel, gold, or other metal grid. Ideal section thickness for transmission electron microscopy with accelerating voltages between 50kV and 120kV is about 30–100 nm. Advances In 1952 Humberto Fernandez Morán introduced cryo ultramicrotomy, which is a similar technique but done at freezing temperatures between −20 and −150°C. Cryo ultramicrotomy can be used to cut ultra-thin frozen biological specimens. One of the advantages over the more "traditional" ultramicrotomy process is speed, since it should be possible to freeze and section a specimen in 1 to 2 hours. References Microscopy Electron microscopy Biological techniques and tools