Paraffin is cooled rapidly after embedding to prevent the formation of which of the following?

• A. Formation of large crystals
• B. Formation of cracks in tissue
• C. Excess shrinkage
• D. Dimensional change

Answer: (A)

Rapid cooling after embedding is used to prevent large paraffin crystals from forming. If cooling is slow, paraffin tends to crystallize into fewer, bigger crystals, which can create a nonuniform, brittle embedding medium and lead to sectioning artifacts such as cracks, chatter, or tears at the tissue–paraffin interface. By cooling quickly, many tiny crystals form, giving a smoother, more uniform block that cuts cleanly and preserves tissue architecture. The other options are less directly related: while processing steps can influence tissue cracking, shrinkage, or dimensional changes, the specific concern addressed by rapid cooling of the embedded block is the avoidance of large crystal formation.