The Opalised Glass, the _Calcedonio_[152] of the Venetians, is obtained by adding the same materials as in the case of the _latticinio_, but in very small proportions: it stands to the latter as weak milk and water to pure milk. In practice, I believe, the opalescence is often given by the addition of phosphate of lime in the form of bone-ash, sometimes, perhaps, by arsenious acid.[153] Pale blue by reflected light, it takes various orange and yellow tints when the light is transmitted through it. Such a vessel as the cylindrical goblet and cover of thick _calcedonio_ in the Waddesdon Room at the British Museum, with a design in high relief representing the Triumph of Neptune, must have been cast in a mould. We now come to certain varieties of glass which were much admired at one time, but are now little in favour. The aim, it would seem, in this class, as in the case of the old Roman prototype, was to imitate various kinds of precious stones and marbles. But the Venetians showed here little of the restraint of their classical predecessors, so that on the whole the colours, where not crude, are huddled together in muddy compounds. An opaque red glass resembling jasper was probably known at Murano as early as the fourteenth century. In an inventory of the property of the Duke of Anjou (_circa_ 1360) there is mention of a ‘_pichier de voirre vermeil semblable a Jaspe_.’ So in the next century, Charles the Bold possessed ‘_Ung hanap de Jaspe garni d’or, à œuvre de Venise_’—to judge from the expression used this beaker was also of glass.[154]