On one of our local beaches you can sit down in any spot and collect half a pound of sea glass from within arm's reach - most of it green, brown and white/clear, some blues and occasional reds/oranges, sometimes marbles or decanter/scent bottle tops, lots of crockery shards too. The village there, across the water from Milford Haven, had 17 pubs in Nelson's time, though now only one - Milford was a hugely important port in those days - so I suspect some of it is pretty old. Parish records show big spikes in births and marriages following major sea battles, as the fleet would come into the haven for refitting and the sailors would go wandering... My partner can never resist sea glass, so we have bucketloads of the stuff. She makes mobiles using it, along with driftwood, shells and beads (recycled from charity shops, plus her own handmade glass beads). We drill the sea glass with a Dremel on a drill stand and cheap diamond tipped bits from China, using a shallow plastic water tray with a lump of blutac to support the pieces of glass and catch any splinters/flakes. High speed, light pressure works best. The glass varies a lot in hardness and the drill bits vary in quality - sometimes they wear out almost immediately, sometimes you can do 30 or 40 with a single bit.
Alan