The page below is a sample from the LabCE course Basic Tissue Orientation and Paraffin Embedding Technique. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Final Steps: Four Through Seven

Add additional molten paraffin after replacing the cassette bottom on top of the positioned specimen and base mold.

A few quick steps will finish the process once the tissue has been oriented.
Step Four: Complete the paraffin block
Add a small amount of molten paraffin to completely cover the grooves or openings in the plastic of the cassette. This will ensure that the specimen and cassette bottom will harden together into a secure block. Avoid air bubbles from being trapped below the cassette bottom as you replace it. Do this by tipping the mold slightly and pushing the trapped air out. Start at one corner of the mold and press any air outward as you replace the cassette.
Step Five: Harden
Move the completed block to the large cold plate to harden. Allow the block to completely cool and harden on the cold plate before attempting to remove it from the base mold. The paraffin of the block will usually appear opaque and white when completely cooled.
Step Six: Scrape
Neatly scrape excess paraffin from the edges of the block to ensure a secure into the block holder of the microtome.
Step Seven: Inspect
Check the block for any obvious defects, such as cracks or air bubbles, before submitting it for microtomy.

Completed block after removing from base mold.