The device has a chromo case extending on width of a flange ring (6) of a pot (1). The ring has an external straight section greater than that of a pot body (7), where the junction between the body and ring is formed by an annular radial shoulder (8). A flexible flat portion of an object is engaged in a passage passing through the ring. The passage emerges, via a lower orifice (12), from a concavity (10) formed in the ring above the shoulder. The concavity has a base extending between the orifice and shoulder with respect to a main axis of the pot along a slope lower than that of the ring.
