What distinguishes crystal from ordinary glass?
The key is powdery red lead oxide and it is Waterford's high lead content (approximately 33 percent) that produces its special sparkle. Other ingredients include ultra-white silica sand, which makes up almost half of the mixture, potash and a small amount of decoloring agents. They arc-mixed together and topped by bits of broken crystal (cullet) taken from earlier rejects. When fired, the cullet melts quickly, helping the raw materials fuse into a molten mass.
Thick-walled ceramic pots, approximately four feet high and three feet in diameter, sit on ledges inside the firebrick furnaces and are gradually heated from underneath by oil flame. Clay is used because it withstands high heat and imparts no color to the glass. The pots last about two weeks before being replaced.
The temperature inside the furnaces is brought to 1,200° C. In about 36 hours the ingredients reach the proper state of melting. A higlu i heat is used for stemware because of the flexibility required in forming, while the arm of a chandelier needs lower heat because it' long, thin shape must cool quickly and set to avoid distortion.