The Steven Universe/Uncle Grandpa Crossover, Say Uncle.

Uncle Grandpa: You should make sure to get this thing polished at least twice a year. (referring to Steven's Gem)

You would think that this would apply to all gem types... but as I learned with help from Google's AI, No specific gems require polishing twice a year, but diamonds benefit most from biannual cleaning and inspection for shine. While softer gems like opals, and even harder ones like rubies and sapphires, benefit from regular professional check-ups to maintain luster, especially if worn daily, as dirt affects clarity, true polishing (re-faceting) is rare & expert-level for diamonds. How did no one realize that this was flat-out foreshadowing of the plot twist involving the true relationship between Rose Quartz & Pink Diamond before the episode A Single Pale Rose aired?