Whatever paraffin formula has been selected for use in your laboratory, its' ultimate performance will be mostly dependent on the melting point and polymerization that occurs as it solidifies through the process of crystallization.
Most manufacturer will provide a list of the ingredients and additives as well as the product melting point on the paraffin media bag or packaging. For example:
- Melting point: 133-136° F (56-58° C)
- Working temperature: 140° F (60° C)
- Water bath temperature: 113-122° F (45-50° C)
- Store below: 86° F (30° C)
A "rule of thumb" however, is that pure paraffin appears almost clear when solid. It is a "softer" paraffin and would be more ideal for sections that are 5 microns (μ) thick. In contrast, paraffin which contains a greater amount of additives or stabilizers will be "harder" and better suited to sections of 2 to 3 µ. However, any paraffin formula performance can be compromised by failing to monitor and control temperatures during the infiltration stage of tissue processing or during the embedding process.