Can you remember what glue you used?
My Gran used to make ornaments from sea shells, usually in the form of frogs because many shells lend themselves to frog-making.
For the Salvation Army Christmas Sale she'd take a large scallop shell and fill it with smaller shell frogs as a choir with their mouths all open singing Christmas carols. An upright scallop mounted at the back would have the opening lines painted on the white surface.
I was fascinated by the ultra fine brush she used for fiddly details. Apparently the shop wanted too much for a fine brush so she gradually cut out the hairs from a bigger but cheaper one and trimmed them to the proper tapered shape. "And as a bonus, on top o' saving money, it's got a decent sized handle for thick clumsy fingers like mine." (They weren't clumsy, just short and spatulate, what I classify as 'artisan fingers' now I know the word.)