This is also an important group of colors, and by far the greatest interest attaches to the red oxides of iron, natural or artificially made. It may be said that of the total output of most paint factories, one-half, or nearly one-half, consists of red pigments in paste form in oil or in red paint ready for use. That is so far as colored pigments are taken into consideration. Therefore we shall begin with the iron oxide reds. Of these the oil color lists as a rule include Venetian red of several shades, Indian red, light and dark, red oxide, maroon oxide and Tuscan red, which has also oxide of iron for its base. Some manufacturers list extended iron oxides under fancy names, as for instance, Pompeiian red, Mars red, Windsor red, Victoria red, etc., etc.
There never has been a standard for purity as to Venetian red, and up to twenty years ago any extended pigment owing its color to red oxide of iron could be placed on the market under that designation. Before the crusade for pure colors in oil began in this country in 1892, it was no uncommon occurrence that Venetian red paint was applied to iron structures that was found on analysis to consist of less than 10 per cent sesquioxide of iron (Fe2O3), the balance of pigment being barytes and whiting.