Resins such as Epon and Spurr harden by which process?

• A. Polymerization
• B. Crystallization
• C. Evaporation
• D. Sublimation

Answer: (A)

Resins like Epon and Spurr harden through polymerization, specifically crosslinking that forms a three‑dimensional network. They begin as liquid monomers or prepolymers mixed with a hardener; when heated or catalyzed, the molecules join covalently to create an infusible, insoluble solid. This is different from crystallization, which relies on atoms arranging into an orderly lattice—epoxy resins cure to an amorphous, glassy matrix rather than a crystalline one. Evaporation would only remove volatile components, not cure the resin. Sublimation is a phase change from solid to gas and has no role in resin hardening. In electron and light microscopy work, this polymerization (crosslinked curing) provides the rigidity and stability needed for thin sectioning.