This is a pressed glass dessert glass called a "ice cup," which was widely used in homes during the Showa era. It was used for things like shaved ice and ice cream. The bottom of the glass has radial cuts, a design feature that beautifully reflects light. There may be distortions or black spots due to the manufacturing techniques of the time, and these are also considered part of the charm of the antique item. My grandmother had this, and I am selling it to organize her belongings. Please understand that this is a used item before purchasing.