What metaphors are used in The Shell Seekers by Rosamunde Pilcher?

An important piece of artwork by Lawrence Stern, The Shell Seekers symbolizes to Penelope her childhood and her time in Porthkerris. When Noel and Nancy blithely suggest to their mother that she sell the piece, it symbolizes how little they care or understand what is important to her. She will eventually donate it to the art museum in Porthkerris, which is where it belongs.