Paraffin temperatures should be maintained within 2° C to 4° C of the melting point of the paraffin. The measure and control of the temperature that the paraffin media is exposed to during its use should be recorded in the quality control records. The consistent maintenance of temperatures in a controlled range will provide the best results and performance from any paraffin formula selected; since at both on the low and high end of the recommended temperature range, problems can occur.
Sectioning of blocks will be easier if the paraffin is cooled at a consistent rate for even solidification of the molten paraffin into its final crystalline structure. Controlled cooling allows the formation of a uniform and homogenous matrix of crystals. Paraffin which cools too rapidly or unevenly can cause grainy textures which interfere with sectioning and may result in artifacts in the final tissue sections. On the other hand, overheating of the paraffin can result in deterioration of the components of the paraffin mixture, and some tissue specimens may become brittle or hardened by prolonged exposure to too hot paraffin.
Some technical problems, which are assumed to be microtomy issues, are really problems with media selection or embedding technique, so it is worth the time to investigate.