Microtomy and Section Preparation
Cutting mechanics
Microtomy quality depends on blade angle, clearance angle, block temperature, and section thickness. Routine paraffin sections are typically 3–5 µm; the clearance angle (the gap between blade facet and block) is usually a few degrees and prevents the blade from rubbing. A dull blade, excessive clearance, or a loose block produces chatter (alternating thick and thin bands).
The ribbon and floatation
A good ribbon is continuous and flat. Sections are floated on a warm water bath (typically around 40–45 °C) to flatten wrinkles, then picked up on a slide. Water that is too hot causes tissue expansion and distortion; too cold leaves folds.
Section artifacts and causes
Candidates must map artifacts to causes: folds from poor floatation; chatter from blade/angle/vibration; holes from incomplete infiltration or bubbles; compression from a dull blade; and knife marks (vertical lines) from nicks in the blade edge. Frozen sections use a cryostat at colder temperatures and are thicker (often 4–8 µm) and less perfect by nature.
Traps
Questions often confuse compression with chatter, or blame the water bath for a problem caused by the blade. Another trap is assuming thicker sections are always easier-beyond a point they wrinkle and float poorly.
Worked rule
If sections show regular parallel thick-thin bands, think chatter: check blade security, reduce clearance angle, and confirm the block is cold and firm. If sections show random holes, think infiltration, not the blade.