Sea glass

Sea glass and beach glass are pieces of glass worn smooth by waves. Technically, "Sea glass" is glass found on beaches along bodies of salt water. As the glass reaches the shoreline pounding waves and rocks break it into smaller pieces. The sharp edges are worn smooth. Salt water erodes the glass and gives it a frosted appearance. "Beach glass" comes from fresh water. It is found mainly along coastlines and the shores of large lakes. However many feel sea glass and beach glass are the same thing. 
Colors.
White, emerald green and brown are the most common colors. They came from jars, plain bottles and beer bottles thrown into the water. Olive green, cobalt blue, aqua and amber are harder to find. They came from medicine bottles, soda bottles and cosmetic jars. The rarest colors are red, orange and yellow. They were originally items such as fine china, streetlamps and even ship lanterns. Many colors are unique to certain periods of history. Small bubbles in the glass help to identify the original glass item.
Locating.
Collectors walk beaches to find sea glass. After plastic became popular for containers it became harder to find sea glass. Sea glass can take from 7 to 10 years to get a frosted appearance. In many places winter seems to be the best time to find sea glass. Experienced sea glass hunters look for periods of low tide to start looking. Beaches that are cleaned of debris regularly won't produce much sea glass. Hunters look for "dirty beaches" that are left alone and have litter.