The recurrent theme in jewellery of the Art Nouveau period was nature and its association with femininity. The aim of Art Nouveau was to evoke rather than portray nature and this was done in an imaginative and creative style. The influence of Japanese art opened the way to stylisation of the natural world and asymmetrical yet fluid lines. It was the first time that the female form appeared as a motif in jewellery. The materials used in Art Nouveau jewellery were selected for artistic merit rather than their intrinsic value and the market saw the introduction of horn, opal, enamel, moonstone, chalcedony, agate and chrysoprase replacing diamonds and precious coloured stones. Another major innovation of Art Nouveau jewellery was the use of plique-a-jour enamel which allowed light to pass through, similar in effect to stained glass.