When you look at the edge of a sharp microtome knife through a microscope you can often see a fine burr running along the edge or a fine crystalline structure running through the metal. Neither edge is good for cutting fine, thin sections. The edge needs to lose the burr and the crystalline effect and become more amorphous and slightly rounded. This can only be achieved by highly polishing the edge. A high polish effect can only be produced by stropping.

Disposable knives
While on this subject one of the problems with disposable knives has always been a high failure rate. Many just don’t cut at all and if you look at the edge of these knives you will often see a burr or the fine crystalline structure just mentioned. The knife edge is just not sufficiently polished.

As funny as it might sound, the edge of these knives can often be recovered, for wont of a better word, if the knife is used to rough cut a block before fine cutting. Rough cutting tends to remove the burr and polish the edge sufficiently for good sections to be obtained or the blade can be stropped before use.