Final answer:
Common treatments of gem corundum include heat treatment, glass filling, and synthetic production, whereas imitations involve the use of moissanite and cubic zirconia among others. Treatments should be disclosed, but often there's asymmetric information where the seller doesn't properly inform the buyer.
Step-by-step explanation:
Some common treatments and imitations of gem corundum include heat treatment and glass filling, which are methods used to enhance the appearance and durability of the gems. Synthetic corundum is also produced, offering a cost-effective alternative with similar physical properties to natural corundum. Imitations such as moissanite and cubic zirconia are frequently used as diamond substitutes, while beryllium treatment can alter the color of sapphires. Doublet corundum, which combines a layer of real corundum with a layer of synthetic or less valuable material, can also be employed for cost savings and visual effect. As for regulations, treatments should be disclosed to the buyer, yet instances of non-disclosure have led to cases of asymmetric information, complicating consumer decision-making.