In epoxy resin processing, a transitional fluid is required.

• A. True
• B. False
• C. Only sometimes
• D. Never

Answer: (A)

A transitional fluid is needed because it acts as a bridge between the clearing solvent and the epoxy resin, allowing the tissue to be infiltrated by the resin effectively. After dehydration, the specimen is cleared with a solvent that is typically compatible with the resin, but epoxy resins are viscous and not directly miscible with many clearing agents. The transitional fluid, which is compatible with both the clearing solvent and the resin, gradually replaces the clearing agent with resin, lowering viscosity and promoting uniform penetration into the tissue. This improves infiltration and reduces artifacts like voids or poor embedding. Without this bridging fluid, resin may fail to infiltrate adequately, compromising block quality.