Eighteenth and nineteenth century varnish formulations and manufacturing processes were based on natural raw materials. Major changes in this period were new pigments or methods of their manufacture: white lead using various heat sources; Prussian blue; artificial ultramarine; zinc oxide (resulting in the use of boiled linseed oil); crimson antimony; lead chromates; cadmium yellow; chromium oxide. In about 1850, ready mixed paints were introduced, with extenders such as talc, whiting and clays.