I was cutting frozen sections of ferret cortex today on a Microtome at 25um. The sections, as far as I could see with my eye, were being sliced ok, but when I pushed back the blade to the starting position after each slice, the blade would scratch the surface of the tissue on the Microtome plate. No matter how I adjusted, rotated, or cleaned the blade, this issue would not go away. The scratches were more than 25um deep since my slice would cleave apart at the scratch. I want to try sharpening the blade.
What is the best way to sharpen the blade by hand?