| 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 |
