PROBLEM |
CAUSES |
Crooked or uneven ribbons |
Edges of knife and block are not parallel |
The four sides of the block are not trimmed parallel |
Wrinkled or compressed sections |
Blunt or dirty knife |
Warm block or knife |
Clearance angle too small |
Thick and thin sections |
Loose knife or loose block |
Clearance angle too small |
Tissue or wax excessively hard |
Areas of calcification present in tissue |
Blunt knife |
Sections adhere to block on upstroke of microtome |
Clearance angle too small |
Blunt or dirty knife |
Ribbons split vertically or scratch lines appear |
Small nicks or dirt on the knife edge |
Clearance angle too large |
Hard material embedded in the wax (grit, dirt, crystals, talc) |
Hard material in the tissue (calcium, crystals, sutures) |
Sections crumble or tear |
Tissue incompletely dehydrated |
Tissue not cleared properly |
Paraffin wax denatured from excessive heating |
Wax has crystallized from slow cooling |
Blunt knife |
Wax too soft |
Wax is contaminated with clearing agent or water |
Section shows areas of varying thickness (‘washboard’ or ‘venetian blind’ effect, chatter) |
Loose knife or block |
Clearance angle too large |
Excessively hard tissue or wax |
Sections will not ribbon |
Clearance angle too small or too large |
Dull or dirty knife edge |
Wax surface too cold |
Section thickness setting too high |
Sections roll up on cutting |
Blunt knife |
Clearance angle too large |
Section thickness setting too high |
Sections disintegrate on water bath |
Water temperature too high, inadequate processing |