Pirate glass is a type of black sea glass that was originally part of very old black glass bottles. Black glass was used to make bottles to hold spirit drinks, as well as other items, but mainly alcohol. The term "pirate glass" was given to black sea glass by collectors and beachcombers, and it harks back to the seafaring nomads of days gone by swigging their rum. Pirate glass is usually dark olive green, often with an air bubble stuck inside which indicates that it was made by hand and thus very old. However, it is important to note that not all black glass is pirate glass, and the black glass found on beaches today generally dates from 1850 to 1920, long after traditional pirates were sailing the high seas.