FAULTS OBSERVED IN TISSUE PROCESSINGFAULTS REASON REMEDY

Brittle or hard tissue

Prolonged fixation Tissue may be softened by soaking in a small dish or bowl containing water with detergent, phenol, or molliflex

Prolonged dehydrationProlonged clearingProlonged paraffin infiltrationOverheated paraffin ovenDrying out of tissue before actual fixation

Clearing agent turns milks as soon as tissue is placed in it

Water not completely removed due to incomplete dehydration

Repeat dehydration with absolute alcohol, then clear again

On trimming, tissue smells of clearing agent

Clearing agent not completely removed due to insufficient impregnation

Block is trimmed down nearest to the tissue. Remaining wax is melted on embedding oven and paraffin impregnation is repeated, changing the paraffin at least once before blocking

Tissue is opaque, section cutting is difficult due to presence of alcohol

Insufficient clearing

Repeat clearing; if object has already been embedded, prolong clearing up to 12 hours the re-embed

Tissue shrinks away from wax when trimmed

Insufficient dehydration therefore incomplete clearing and impregnation

Repeat the whole procedure

Tissue is soft when block is trimmed

Incomplete fixation

Repeat the whole procedure

Air holes found on tissue during trimming

Incomplete impregnation

Repeat impregnation

On trimming, wax appears crystalline

Contaminated wax

Re-embed in freshly filtered waxBlock not cooled

rapidly enoughParaffin block, after cooling, is moist and crumbles

Insufficient paraffin impregnation

Repeat paraffin impregnation, then re-embed

FAULTS OBSERVED IN TISSUE CUTTINGFAULTS REASON REMEDY

Section fail to form ribbons

Surfaces and edges of the block are not parallel

Re-trim the block

Horizontal surface of the block is not parallel to the knife

Readjust and re-orient the block

Paraffin wax is too hard

Coat horizontal edges of the block with wax of lower melting point

Knife is tilted too much

Reduce the tilt

Sections are too thick

Readjust the thickness of the sections

Knife is dull Hone and stropSection roll up on cutting so that they adhere and get broken against the knife edge

Knife is blunt Sharpen the knifeTilt of knife is too great

Reduce the tilt

Knife edge is dirty

Clean the knife edge

Ribbon is curved, crooked, or uneven instead of straight

Blunt of dull spot on the knife, producing an irregular knife edge

Adjust the knife so that knife edge will present a uniformly shard edge to the block, or sharpen

Edges of block are not parallel but round or wedge shape

Re-trim the block

Knife is not parallel to the block

Readjust the knife and block

Paraffin is impure

Repeat impregnation using pure wax

Sections are compressed, wrinkled, or jammed

Knife is blunt or dull

Re-sharpen the knife

Paraffin block is warm and soft

Cool the block on ice water until firm

Knife edge is coated with paraffin

Clean the knife edge

Sections are too thin

Readjust thickness of section

Microtome set screw is loose

Tighten the screw

Tilt of knife is too vertical

Reduce the tilt

Sections are squashed (width of each section is less than that of block)

Bevel of knife is lost due to incorrect sharpening

Re-sharpen using a knife back or automatic knife sharpener

Hole is formed in the section

Bubble or dirt formed in the embedding medium

Re-embed in freshly filtered wax if necessary

FAULTS REASON REMEDYHard spot in tissue due to calcium

Once embedded in paraffin wax, decalcification is impractical; use base sledge microtome with a wedge knife

Sections of unequal thickness are produced

Tilt of knife is too great or bevel is not cleared, hence object is compressed against the knife edge

Reduce the tilt

Clamp set screw in knife or block holder is loose

Tighten the screw

Blocks are too large

Cut blocks into small fragments

Blocks are too hard

Soften the blocks in detergent or phenol

Sections adhere to the knife or other parts of the microtome

Static electricity due to low atmospheric humidity

Breathe out or blow gently on the block and knife to breakup static electricity, or boil water in the room to increase the humidity

Knife edge is dirty

Clean the knife edge

Knife edge is dull Sharpen the knifeKnife tilt is too great

Reduce the tilt

Ribbon is split or lengthwise vertical scratches are seen on sections

Nicks or damage on the knife edge

Sharpen the knife

Dirty embedding Re-embed in filtered wax

Knife edge is dirty

Clean the knife edge with xylol

Tilt of knife is too great

Reduce the tilt

Sections are lifted from the knife on upstrokes

Knife tilt is too great

Reduce the tilt

Knife is dull Sharpen the knifeParaffin is too soft or room temperature is warm

Cool paraffin wax in ice water

Resistance is felt on the lower part of the section during cutting

Tilt of the knife is too small, paraffin block is therefore compressed against the base of the knife towards the end of stroke

Increase the tilt

FAULTS REASON REMEDYHorizontal or parallel lines or furrows across the section (“Chatters”) are seen, forming thin and thick zones

Knife edge vibrates due to hardness of tissue

Treat with phenol during processing or collodionize

Tilt of knife is too great

Reduce the tilt

Section cut is sometimes thin, sometimes thick

Knife is blunt Sharpen the knifeKnife is not clamped properly

Adjust the knife

Tilt of knife of block holder is loose

Tighten adjusting and locking screws

Knife tilt is too small that block is compressed by bevel and section is not cut

Increase the tilt

Knives make a hard metallic scraping or ringing sound on backstroke, when section is cut

Tilt of knife is too slanted

Readjust the angulation of the knife

Tissue is too hard

Take fresh block treated with phenol during processing

Knife blade is too thin

Change the knife

Frozen tissue crumbles and comes off the block holder when cut

Freezing is not adequate

Refreeze the tissue block

Frozen tissue chips into fragments when cut

Tissue is frozen too hard

Warm the tissue with fingers