FAULT/PROBLEMS OBSERVED - REMEDY

Tissue may be softened by soaking in a small dish or bowl containing detergent, phenol or Molliflex.

Brittle or hard tissue

Repeat dehydration with absolute alcohol then clear again.

Clearing agent turns milky as soon as tissue is placed on it.

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

On trimming, tissue smells of clearing agent.

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

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

Repeat the whole procedure.

Tissue shrinks away from wax when trimmed.

Repeat fixation

Tissue is soft when block is trimmed.

Repeat impregnation

Airholes found on tissue during trimming.

Re-embed in freshly filtered wax.

On trimming, wax appears crystalline.

Repeat paraffin impregnation, then re-embed.

Paraffin block after cooling is moist and crumbles.

Re-trim the block.

Sections fail to form edges of the block ribbons due to surfaces and edges of the block is not parallel.

Re-adjust and re-orient the block.

Sections fail to form edges of the block ribbons due to horizontal surface of the block is not parallel to the knife.

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

Sections fail to form edges of the block ribbons due to paraffin wax is too hard.

Reduce the tilt.

Sections fail to form edges of the block ribbons due to knife is tilted too much.

Readjust the thickness of the sections.

Sections fail to form edges of the block ribbons due to sections are too thick.

Hone and strop.

Sections fail to form edges of the block ribbons due to knife is dull.

Sharpen the knife.

Sections roll up on cutting so that they adhere and get broken against the knife edge due to knife is blunt.

Reduce the tilt

Sections roll up on cutting so that they adhere and get broken against the knife edge due to the tilt of knife is too great.

Clean the knife edge.

Sections roll up on cutting so that they adhere and get broken against the knife edge due to the knife edge is dirty.

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

Ribbon is curved, crooked or uneven instead of straight due to blunt or dull spot on the knife, producing an irregular knife edge.

Re-trim the block.

Ribbon is curved, crooked or uneven instead of straight due to edges of the block are not parallel but round or wedge shaped.

Readjust the knife and block.

Ribbon is curved, crooked or uneven instead of straight due to the knife is not parallel to the block.

Re-sharpen the knife.

Sections are compressed, wrinkled or jammed due to knife is blunt or dull.

Cool the block on ice water until firm.

Sections are compressed, wrinkled or jammed due to paraffin block is warm and soft.

Clean the knife edge.

Sections are compressed, wrinkled or jammed due to knife edge is coated with paraffin.

Readjust thickness of the section.

Sections are compressed, wrinkled or jammed due to sections are too thin.

Tighten the screw.

Sections are compressed, wrinkled or jammed due to microtome set screw is loose.

Reduce the tilt.

Sections are compressed, wrinkled or jammed due to tilt of knife is too vertical.

Re-sharpen, using a knife back or automatic knife sharpener.

Sections are squashed (width of each section is less than that of the block) due to the bevel of knife is lost due to incorrect sharpening.

Re-embed in freshly filtered wax if necessary.

A hole is formed in the section due to bubble or dirt formed in the embedding medium.

Re-process tissue.

A hole is formed in the section due to tissue is not processed properly and will not form a section (especially if center is raw).

Re-process tissue

A hole is formed in the section due to under-processed portion of tissue bursts on contact with warm water.

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

A hole is formed in the section due to hard spot in tissue due to calcium.

Tighten the screw

Sections of unequal thickness are produced due to clamp set screw on knife or block holder is loose.

Cut blocks into smaller fragments.

Sections of unequal thickness are produced due to blocks are too large.

Soften the block in detergent or phenol.

Sections of unequal thickness are produced due to blocks are too hard.

Reduce the tilt.

Sections of unequal thickness are produced due to tilt of knife is too great or bevel is not cleared, hence object is compressed against the knife edge.

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

Sections adhere to the knife or other parts of the microtome because of static electricity due to low atmospheric humidity.

Clean the knife edge.

Sections adhere to the knife or other parts of the microtome due to knife edge is dirty.

Sharpen the knife.

Sections adhere to the knife or other parts of the microtome due to knife edge is dull.

Reduce the tilt.

Sections adhere to the knife or other parts of the microtome due to knife tilt is to great.

Reduce the tilt

Sections are lifted from the knife on upstrokes due to knife tilt is too great.

Sharpen the knife.

Sections are lifted from the knife on upstrokes due to knife is dull.

Cool paraffin wax in ice water.

Sections are lifted from the knife on upstrokes due to due to paraffin is too soft or room temperature is warm.

Increase the tilt.

Resistance is felt on the lower part of the section during cutting due to the tilt of knife is too dull; paraffin block is therefore compressed against the base of the knife towards the end of stroke.

Treat with phenol during processing or collodionize.

Horizontal or parallel lines or furrows across the section (“chatters”) are seen because of knife edge vibration due to hardness of tissue.

Reduce the tilt.

Horizontal or parallel lines or furrows across the section (“chatters”) are seen due to tilt of knife is too great.

Sharpen the knife.

Section cut is sometimes thin, sometimes thick due to knife is blunt.

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

Section cut is sometimes thin, sometimes thick due to knife is not clamped properly.

Tighten adjusting and locking screws.

Section cut is sometimes thin, sometimes thick due to knife or block holder is loose.

Increase the tilt.

Section cut is sometimes thin, sometimes thick due to knife tilt is too small that block is compressed by bevel and section is not cut.

Readjust the tilt.

Knife makes a hard metallic scraping or ringing sound on backstroke, when section is cut due to tilt of knife is too slanted or too big.

Take fresh block treated with phenol during processing.

Knife makes a hard metallic scraping or ringing sound on backstroke, when section is cut due to tissue is too hard.

Change the knife.

Knife makes a hard metallic scraping or ringing sound on backstroke, when section is cut due to knife blade is too thin.

Refreeze the tissue block.

Frozen tissue crumbles and comes off the block holder when cut due to freezing is not adequate.

Warm the tissue with fingers.

Frozen tissue chips into fragments when cut due to tissue is frozen too much.

Adjust the block holder to make the block edges parallel to the knife.

Ribbons are crooked because the top and bottom edges of block are not parallel to edge of blade/sides of block are not perpendicular to the blade.

Microtome needs recalibration.

Sections are too thick due to wrong micrometer setting.