Crooked paraffin ribbons may be caused by

• A. Nonparallel block horizontal edges
• B. Dull blade edge
• C. Too high embedding temperature
• D. Excess mounting medium

Answer: (A)

Crooked ribbons come from misalignment of the tissue block relative to the knife. When the horizontal edges of the embedded block aren’t parallel, the blade engages the block at slightly different angles from one cut to the next. That small change in cutting angle twists the ribbon as it separates from the block, producing a crooked appearance. The remedy is to ensure the block faces are square and parallel to the knife edge and stage, trimming or re-embedding as needed and checking that the block sits true in the mold.

Dull blade edges tend to produce ragged, torn, or chattered surfaces rather than a consistently crooked ribbon. Too high embedding temperature softens the paraffin and can distort tissue shape, but that doesn’t specifically cause a crooked ribbon. Excess mounting medium can cause adhesion issues or extrusion around the tissue, but the main cause of crooked ribbons is block misalignment.