The different colors of glassware from the Verrerie de Biot are obtained using dyes based on sulfur, manganese oxides, iron, nickel, cobalt, chromium, copper, etc. The clearer glasses are made by eliminating these dyes or compensating for the coloring they provide. The excess iron content of certain sands, for example, gives the finished glass a sometimes detrimental greenish color. To qualify the transparency of the glass, the glassmakers use opalizers such as fluorine and phosphates.