DETROIT — It may have once been part of a beer bottle. Or a vase. Or a Milk of Magnesia container.

But after decades of being tumbled by water, after years of having its edges softened and rounded, it sits on the beach, a colored shard of tan or turquoise refracting the sunlight.

Once part of a whole object, it has become its own entity: sea glass.

These pieces created by humans for function have been reclaimed by water, tossed by the lakes and seas and given back to us as fragments of beauty. And now as the weather warms, beachside residents — and tourists — are blessed with the possibility of days spent by the beach hunting sea glass.

But what do you look for? How do you get started? What colors should you seek? How do you turn it into decor or jewelry?

To help out, we've put together this sea glass primer:

Pure sea glass consists of pieces that have broken apart from lanterns, headlights, bottles and other glass items that were dumped or thrown into lakes and oceans. Over 15 to 60 years, and sometimes for more than a century, the forces of waves, sand and stone have rounded the sharp edges of these glass shards to create smooth, translucent shapes.

Sea glass is best found on pebbly or stony beaches about 10 feet from the water line. "You will almost never find sea glass on a sandy beach," says Cindy Kuhn, 55, of Columbus, Ohio, a jeweler who has been collecting sea glass for five decades.

She adds that it's wonderful to go hunting "after a storm because water gets churned up."

Linda Mickevicius, 56, has been collecting sea glass along Michigan's shores for the past seven years. She recommends looking for "a nice gravel wash along the shore."

The shores of Lake Erie, where Kuhn began collecting as a young girl, are also rich in sea glass.

One of the most famous sea glass beaches in America is Glass Beach in Fort Bragg, Calif., which was once a public dump and is now covered with sea glass. Visitors must only admire, though, because California State Parks has taken over the site and prohibited collecting.

Sea glass colors serve a purpose beyond aesthetics. Sea glass colors matter because they signify rarity. Kuhn and Mickevicius, both active members of the North American Sea Glass Association, say orange is the rarest color. Kuhn says orange glass could have come from decorative glassware like goblets, candy dishes and decanters.

Pinks, reds and yellows follow as the next rarest. After that comes kiwi and lime green, lavender, sky blue and turquoise. Next come cobalt blues. The most common colors are kelly green, rich brown and white — not just because of beer bottles but also because of old medicine and bleach containers.