Which resin yellows as the preparation ages?

• A. Natural resin
• B. Synthetic resin
• C. Both natural and synthetic
• D. Neither natural nor synthetic

Answer: (A)

Natural resins tend to yellow as they age because their components are susceptible to oxidation and photo-oxidation. In media like Canada balsam, the natural terpenoids and other constituents slowly react with oxygen and light to form colored compounds, producing an amber to brown discoloration over time. Synthetic resins, on the other hand, are designed to form stable, highly cross-linked networks that resist such aging changes, so they remain clearer for longer. So, the resin that yellows with aging is the natural resin.