Sea glass begins as normal shards of broken glass that are then persistently tumbled and ground until the sharp edges are smoothed and rounded. In this process, the glass loses its slick surface but gains a frosted appearance over many years.
Naturally produced sea glass ("genuine sea glass") originates as pieces of glass from broken bottles, broken tableware, or even shipwrecks, which are rolled and tumbled in the ocean for years until all of their edges are rounded off, and the slickness of the glass has been worn to a frosted appearance. Artificially produced sea glass (sometimes called "beach glass"), although superficially similar to sea glass in appearance, nevertheless has clear differences in appearance. Having not actually originated from the sea, most connoisseurs will not consider artificial "sea" glass to actually be genuine sea glass, but rather simply tumbled glass, where pieces of modern day glass are tossed into a rock tumbler or dipped in acid to produce the desired finish. Artificially-produced, the glass is much less expensive and is used for making jewelry, but is often passed off as real sea glass.