Crooked ribbons in paraffin sections are most likely due to nonparallel horizontal edges of which component?

• A. Block
• B. Knife
• C. Coverslip
• D. Slide

Answer: (A)

Crooked ribbons occur when the cutting plane isn’t consistent across the block because the block itself isn’t perfectly flat. If the horizontal edges of the paraffin block aren’t parallel, the surface that the knife engages changes along the block as you advance, so each ribbon can come off at a slightly different angle or thickness. The result is ribbons that appear skewed or bent. To prevent this, trim the block to create flat, parallel faces and ensure the tissue is properly oriented within the block. The knife can cause other artifacts if it’s dull or damaged, but the specific issue of crooked ribbons points to the block’s edge geometry, not the coverslip or slide.