Unplug your lamp and remove the shade. Wipe the base of the lamp with a damp cloth to clean it. Clean your shells if you collected them on the beach. Boil them and scrub them with a toothbrush to remove all sand, grit and odors left behind by former residents.
Plug in your hot glue gun and pipe some glue around the edges of a shell. Place the glue side of the shell against the lamp, starting at the bottom of the lamp. Add more shells to fill in the bottom row around the whole lamp.
Glue on another row of shells. If you're using hinged shells, such as scallops or bi-valve clam shells, overlap the thin side -- or the lip -- of the shell slightly on the row below it. If not, nestle them close together, with the side you like best facing outward.
Continue covering the lamp row by row, working your way to the top. If there are any gaps or spaces you wish to cover, and a cluster of small shells in the spot to fill it in.
Glue a row of shells to the lamp shade, if desired. Glue a row of shells around the bottom edge to tie the look together.
Take your lamp and shade outdoors. Spray it with a coat or two of clear acrylic sealer or spray varnish to protect the shells and keep them looking shiny and lustrous. Allow them to dry according to the spray manufacturer's instructions.
Re-attach your lamp shade and plug in your lamp.