Clarice shows Colley Shorter a piece that she has made from scraps of clay pilfered from the factory. Colley taps it and it gives a dull ring. Unfired clay would not sound like that.
Clarice is seen at home modelling some clay before an open fire. As a ceramics worker it is extremely unlikely that she would do this as she would know that the heat from the fire would dry out the clay, making it increasingly difficult to work with.