Final answer:
True gemstones should be natural and not treated without disclosure to buyers, as undisclosed treatments can lead to asymmetric information in the gemstone market.
Step-by-step explanation:
Ideally, true gemstones should be authentic, rare, and naturally beautiful, but they should not be treated without disclosure. Treatments like oiling or applying epoxy, as in the case with some emeralds, or irradiation used on diamonds, topaz, and tourmaline to enhance colors, are common practices.
However, such treatments should always be disclosed to buyers, but unfortunately, this information is sometimes withheld, leading to a situation of asymmetric information in the market. True gemstones like ruby and emerald gain their color from traces of Cr³+ impurities, indicating that even natural gemstones can have imperfections that contribute to their beauty.