But the clues to that oceanic treasure hunt are becoming harder to find. Sea glass - those rounded, frosted shards that once held milk or medicine or seltzer - is disappearing.
"Between recycling and the use of plastic, there just isn't a lot of glass anymore," said Richard LaMotte, often referred to as the "Father of Sea Glass" since the 2004 publication of his book Pure Sea Glass: Discovering Nature's Vanishing Gems.
The book includes not only tips for finding sea glass, but history, appraisal techniques, and a detailed color analysis. Yellow, for example, was primarily used for tableware, and one type was produced with 2 percent uranium dioxide, giving it a neon glow under ultraviolet light.
"A lot of people go out to look for it, and it's still there, but there's a lot less of it," LaMotte said.
Sea glass is formed in a two-part process. First, the alkaline pH of the water strips off the surface gloss and corrodes the outer layers of each piece. Then the waves and sand act as a sandblaster, softening sharp edges and pitting the surface, said Richard Baldwin, a research chemist for NASA in Cleveland. He collects antique bottles and became interested through his collections in the corrosion process.
The softer and cheaper the glass - such as bottle glass, for example - the faster it corrodes and softens, Baldwin said. Still, it takes 20 to 30 years for the ocean to turn a cracked champagne bottle into a frosted, rounded piece of pure sea glass.
LaMotte said he visits his favorite glass spots about once a week now. As he spoke, his hands reached down to the sandy, stony ground at a beach behind a friend's house across from Baltimore's Inner Harbor. After an hour, he had collected a square from a 1960s Sprite bottle (with its two telltale bubbles at the bottom), a brown, comet-shaped piece from a 1947 beer bottle, and a tiny turquoise teardrop.
Because most sea glass comes from bottles, clear, brown, or green pieces wash up most often. But in Maryland, there were a couple triangles of lime, a dash of citron, and a tiny dot of cobalt blue, most likely from the Bromo Seltzer bottles that used to be produced across the bay.
Red, yellow, and orange are the rarest colors, along with black, which often glimmers dark green under a flashlight.
LaMotte began hunting for glass about two decades ago, when his wife, Nancy, wanted to incorporate sea glass into her jewelry. During the day, he is a vice president at his family's water-treatment company in Chestertown, but on weekends, he wanders beaches and bays. He became interested in the history behind the bits and pieces and wanted to know more about the "frosting" caused by the saltwater corroding the glass surface.
There's such a demand for the glass, both for jewelry and as collector's pieces, that a black market has developed, LaMotte said. Instead of finding the glass organically, people will use a rock tumbler and various tricks to make glass appear old and pitted. Why? A good red or orange piece can bring hundreds of dollars.
"Over the last 10 years, [collecting sea glass] has kind of exploded," he said. "People enjoy getting out in nature. They realize it's vanishing; there's not much left. And then there are the colors of it; there are so many of them . . . and it's cool to see what Mother Nature does with a piece of glass."
Terri Kirby Hathaway, the marine education specialist for the North Carolina Sea Grant Association, said much of today's glass comes from past dumping of beer and soda bottles into the sea. There is a lot of sea glass in Boston Harbor, for example, because the islands in the harbor were used as a dump for years; as erosion occurred, the glass appeared.
But as people have become more environmentally aware, they have stopped dumping glass and started recycling. Also, the federal Ocean Dumping Ban Act of 1988 officially banned dumping waste into the oceans.
"I've lived on the coast for 28 years, and finding glass on a beach here is pretty rare now," Hathaway said. "I might find one piece a week now. So now I like to look for toys, like those little Army men, or I found the monkeys from the Barrel Full of Monkeys game."
True sea glass "snobs" take only pieces that are completely frosted and well rounded - no sharp edges for them. They'll shove rejects back in the sand or toss them back into the sea for another few rounds of rough-and-tumble.
Some people prefer thicker glass, others older glass - defined by the bubbles that disappeared when glass production was automated in the 1920s.
LaMotte, Hathaway, and Minopetros all have their own special spots to find glass but say it takes time to train the eye to see it.
"I went to Sea Bright and found three good bags," Minopetros said. "But sometimes, other people come with me, and they don't see it."
Sea Glass Fast Facts
Orange, red, turquoise, and yellow shards are the hardest to find. Rare colors come from tableware.
Green, brown, and white/clear are the most common colors. They come from mass-produced bottles made after the 1920s.
Bubbles usually indicate older glass. Use a flashlight to detect them.
To find sea glass, skip the main beaches. Check out grassy areas and among rocks, which are more likely to catch them. Bay sides are often better for finding glass than beach sides, as in Cape May. Check out the tide charts and go around low tide, but sometimes the high-tide line can be lucrative.
Source: Richard LaMotte
Contact Dawn Fallik at firstname.lastname@example.org. This article and video were written as a part of "The View from the Beach" series, which is partly funded by the University of Delaware.