Reasons why a ribbon may not form:
(1) The paraffin is too hard (see next).
(2) The clearance angle of the knife (tilt) is too large.
(3) The knife edge is dull.
(4) The sections are too thick.
The paraffin may be too hard if:
(1) The room is too cold.
(2) The paraffin has too high a melting point (“harder”) for the conditions.
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Problem
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Suggestion
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room too cold
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Increase the room temperature, warm the block or knife, use a lamp that generates heat near the microtome, etc.
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paraffin too hard
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Use a paraffin that melts at a lower temperature (“soft”). Or coat the block with a rim of softer paraffin (primarily on the upper and lower edge of the block as it sits in the microtome.
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clearance angle too great
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Reduce the clearance angle.
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sections too thick
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Reduce the thickness of the sections.
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knife edge dull
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Resharpen knife or use a new disposable blade.
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If a ribbon is almost forming (but not quite) then:
(1) Try to unroll the first section with a fine brush.
(2) Hold the unrolled section down lightly.
(3) Cut another section and repeat.
If a few sections can be held down then a ribbon may be started.
