Ribbons split vertically or scratch lines appear

A section of endometrium stained H&E showing a tear, in this case caused by a small focus of calcium.

Reasons for scratch lines are:

• small nicks in the knife edge which can be caused by handling the knife badly or by hard material embedded in the wax or contained in embedded tissue.

• If the knife clearance angle is too great a build up of debris can occur on the knife edge, and that debris can cause scratch lines in sections rather than the clearance angle itself causing scratch lines to appear.

• Hard material embedded in the wax (grit, dirt, talc). If this does happen then the only solution is to filter the melted wax before use. Most modern waxes are very clean but occasionally one can get a batch that has a fine grit in it. We tend to filter all of our wax before use as a routine.

• Hard material in the tissue (calcium, crystals, sutures) as was the case in the previous slide. If the material is calcium surface decalcifying the block will overcome the problem. If its crystals you will need to identify the type before being able to remove them. Things like sutures should not have been left in the tissue in the first place and they really do destroy a knife edge very quickly.