I find all my sea glass in the central coast of California. Dark sage green sea glass set in 14k yellow gold fill with silver backs.
Gold-filled jewelry has 100x more gold alloy than gold plated and because that layer is so much thicker, it means gold-filled jewelry lasts longer and stands up to wear and tear better than gold plated. All it would take is one small scratch on a gold-plated piece to expose the jeweler's brass underneath. As long as the piece is well cared for, gold-filled jewelry can last a lifetime.