One bright fall morning last year, my daughters and I stood in a long line at the North American Sea Glass Festival in Lewes, Del., our precious find clutched in my hands. We had zipped through the display rooms to the outdoor tent where collectors were already waiting, holding plastic baggies of colorful glass. This was the “shard identification booth,” the sea glass world’s version of “Antiques Roadshow,” though the men behind the table, members of the Delmarva Antique Bottle Club, looked more like retired farmers than fine arts experts.

A visitor walking by scoffed. “It’s not worth anything,” he said. “Get out of line.” But despite the amazing hues we saw around us, we held out hope for our find: A frosted, 2-by-2-inch piece of what looked like cut crystal that we had found the previous Thanksgiving at nearby Rehoboth Beach, glittering alone on the packed wet sand, a gift from the sea.

We were quite disheartened after our long wait, then, to learn from expert Peter Beaman that what we had found was not cut crystal but more likely pressed glass, probably from the 1920s or ’30s. But our disappointment dissipated as we focused on the collections and vendors at that third annual sea glass festival.

Sea glass collecting — gathering sea-smoothed pieces of old broken glass — was once considered an arcane hobby. Now it’s becoming a national obsession. The New Yorker magazine recently ran a cartoon showing one person saying to another, “You are my blue beach glass.” (Though any true aficionado knows that red is much rarer than blue.)

The North American Sea Glass Association had planned on 1,000 visitors a day at last year’s event, said author and expert Richard LaMotte, but wound up selling more than 4,000 tickets. And the group expects healthy attendance at this year’s festival, to be held Oct. 17 and 18 in Erie, Pa.

So what do you do at a sea glass festival, besides be disabused of the notion that you’ve found a priceless shard? You can buy jewelry or just walk around admiring what some folks can do with a piece of glass and some metal or wire. (My mother, the girls and I were entranced by the cell phone charms — surely among the newest decorative uses for sea glass — and by an old window transformed into art by hundreds of pieces of glass glued to its panes.) You can listen to lectures on glass identification or enter the “shard of the year” contest, which drew hundreds of entries last year. (The $1,000 first prize went to Linda Boehm, of New York, who had found what appeared to be the top half of a red bottle stopper.)

But mostly, if you, like me, walk on the beach with eyes permanently downcast, sweeping the sand for a promising glint, it’s similar to attending a Whatever Anonymous meeting, with people freely confessing their addiction and receiving total understanding. A documentary called “From Breath and Fire,” shown in the standing- room-only tent, mesmerized the crowd, which laughed in self-recognition at collectors owning up to trespassing on private beaches in search of colorful loot.

Sharon Umbaugh flew in from Hawaii with more than 32,000 pieces of glass in bundles of 400 last year and estimates that she sold half of them at $30 apiece. The collector, who makes her living selling sea glass from her Web site and plans to attend the Erie festival, said she was curious last year to see the difference between pieces of East Coast and Hawaiian sea glass. “Because of the high surf in Hawaii, the glass becomes smoother and more rounded,” she said, “so they will look more like jelly beans.”

The Great Lakes can produce yet another kind of glass, said LaMotte, who added that one should “keep in mind everybody up there calls it beach glass, not sea glass.” The lake glass comes from dumps along the shoreline or from heavy shipping traffic. Because the glass is more contained by the lakes and can be repeatedly washed against rocky shores, some pieces there are smaller, more pebble-size, he said.

The Erie festival will feature more than 40 vendors and lectures on new subjects, such as sea glass marbles, which may be the remainders of ships’ ballast. But many attendees will be there for the simple pleasure of it.