Watch during the scene where the step-mother and sisters are at the dinner table and talking about this "mystery women" that the Prince is falling for. Danielle goes to refill her step-mother's glass and she clumsily tips it over...But when it hits the table it has the unmistaken sound of plastic. Was plastic even around in the year 1518??
I agree. The color of the cup also looks like it's made of horn, probably carved out of a cow-horn, which is the way people made cups from the stone-age up to the industrial revolution.