Technically pastel is an art medium; powdered pigments mixed with a small percentage of binding that commonly come in the form of sticks. The interest for artists remains in the accuracy of its color effect compared to the natural dry pigments. Although revealed by Leonardo da Vinci, it is only in the 18th century that pastels became a fashionable medium. Used in a mixture with gouache, pastel art was a frequently used for portraits in Europe, it was only a century later that the American artists started using the medium. From Edgar Degas, who mastered the technique, to Fernando Botero artists have always enjoyed using pastel painting for its unique palette of colors.