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The page below is a sample from the LabCE course Microtomy of Paraffin-Embedded Tissue. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Block edges are not in line with the blade.

Troubleshooting Common Microtomy Problems

Microtomy problems do not disappear with experience, but experience does allow the microtomist to identify and troubleshoot the problems quickly. Below is a summary of the most common problems that can be identified at the microtome. Many microtomy problems have several sources, so it is best to address them one at a time until the problem is resolved.
Microtomy IssueSymptom/SourcePossible Resolution
Ribbon will not form
Sections curl, skip, or stick to top of block; ribbon separates easily
  • Paraffin too hard; needs to be stickier
  • Room/block too cold/hot
  • Sections too thick
  • Cannot seem to anchor the ribbon
  • Angle of knife clearance is too small
  • Blade may be caked and dirty
  • Something in microtome not clamped down securely
  • Choose paraffin with lower melting point
  • Adjust room temperature
  • Decrease microns
  • Dull blade slightly; introduce nick to one edge of blade
  • Increase clearance to angle between 3-8 degrees
  • Replace with clean blade
  • Tighten all clamps
Crooked ribbons
Straight ribbons difficult to form
  • Top & bottom edges of block not parallel to edge of blade/sides of block not perpendicular to blade
  • Block face uneven; one edge is coarse-faced before the rest of the block
  • Adjust the block holder to make the block edges parallel to knife
  • Block holder must be aligned so that top and bottom of block are parallel to blade and sides of block must be perpendicular to blade
Ribbons compress and crumple
Smooth ribbons do not form
  • Block is too warm
  • Slow and uneven rotations increase compression
  • Paraffin is too sticky; needs to be harder
  • Dull knife
  • Knife clearance is too small
  • Block must be chilled well
  • Use consistent wheel rotation to get even ribboning
  • Need paraffin with higher melting point
  • Change to fresh blade
  • Increase knife clearance
Large holes, missing tissue, or mushy sections
Parts of tissue not showing on slides
  • Tissue not embedded flat; will not show during sectioning
  • Tissue not processed properly and will not form a section (especially if center is raw)
  • Under-processed portion of tissue bursts on contact with warm water
  • Block faced too aggressively
  • Depending on issue/symptom, re-embed or re-process tissue as required
Ribbons stick to microtome or clothes
Ribboning is difficult because sections attract themselves to everything
  • Static electricity
  • Use anti-static spray; cut smaller ribbons for better control; to avoid creating static, do NOT wipe microtome frequently and/or vigorously, especially with ParaPel®
Knife gouges out part of block
Blade chops into block; tissue may be lost
  • Tissue is loose in block
  • Block not securely embedded to cassette
  • Knife/other microtome parts not clamped down
  • Block is not secure in block holder
  • Aggressive facing with rapid wheel rotation
    • Re-embed tissue
    • Re-embed block to properly secure to the cassette
    • Tighten all clamps to verify all parts are properly secured
    • Re-secure block in block holder
    • Slow down