Shannon – In cutting sections of tissue embedded in paraffin wax blocks, if the tissue section or ribbon of wax sections contains thick and thin zones parallel to the knife edge on the section, this is called chatter or venetian blind effect. It can be caused by the block or knife being loose in the holder so, to correct this, tighten the knife or block screws. If it should be due to an excessively steep knife angle, reduce the angle to an appropriate level.