You may perhaps have thought yourself very hardly treated in being obliged to begin your natural history drawing with so delicate a thing as a feather. But you should rather be very grateful to me, for not having given you, instead, a bit of moss, or a cockle-shell! The last, which you might perhaps fancy the easiest of the three, is in reality quite hopelessly difficult, and in its ultimate condition, inimitable by art. Bewick can engrave feathers to the point of deceptive similitude; and Hunt can paint a bird’s-nest built of feathers, lichen, and moss. But neither the one nor the other ever attempted to render the diverging lines which have their origin in the hinge of the commonest bivalve shell.
John Ruskin, Laws of Fesole, 1877-9

Ruskin collected this shell on a visit to Venice. In Fors Clavigera, he writes that he picked up a ‘little grey cockle-shell … out of the dust of the Island of St Helena; and a brightly-spotted snail-shell, from the thistly sands of Lido; and I want to set myself to draw these, and describe them, in peace.’ His diary for 16th November 1876 notes ‘Better after staying in all day resting, and painting cockle shell successfully; getting rhythms also into form.’