Tassies were created using a moulding process. The models for his replicas were crafted by fine artists of the day and included classical subjects, proverbs and portraits of royals and other noted personalities. The contemporary portraits were modeled from life whenever possible and cast in white enamel then mounted upon a darker color background. The wide variety of subject matter and detailed execution made tassies popular with collectors.
James was succeeded by his nephew William (1777-1860) and later by James Wilson. Various other companies copied the idea and literally hundreds of thousands of these glass replica cameos and intaglios were made. Some of those made by James carry a mark 'T' or 'Tassie F', the ones made by William are marked 'W Tassie F'. In addition, Tassie made casting models for Josiah Wedgwood to use in creating his jasperware cameos.