- PMMA (polymethyl methacrylate) e-beam resist marked “expired 2012” was successfully used, prompting discussion on whether expiration dates for such materials are meaningful.  
- Solvent evaporation (anisole in this case) rather than polymer degradation was identified as the primary aging mechanism, leading to higher viscosity and thicker films rather than loss of function.  
- Chain-length shortening via random lysis was proposed as an alternative degradation pathway, though no evidence of performance loss was observed.  
- Practical tip: once opened, bottles should be tightly resealed to slow solvent loss and maintain resist specifications.  
- The exchange illustrates how open-source/hobbyist labs can safely extend the usable life of microfabrication chemicals beyond manufacturer-stated dates through empirical testing.