Regular glass is fragile yet hard. It is transparent. The primary ingredient is silicates, commonly known as sand. Glass also typically includes soda ash and limestone. When exposed to high temperatures, the materials fuse. The new material is then cooled rapidly to become rigid. Glass is solid, hard, fragile and can create shards when broken; it is inert, transparent and it is recyclable.
Another ingredient that can be added to glass is lead. It is recognised for the way it reflects light.
The ingredients to create lead glass are between 54 and 65 per cent SiO2, 13 and 15 per cent Na20 (soda ash), 18 and 38 per cent PbO (lead oxide), K2 (potash) and additional oxides. If less than 18 per cent of lead oxide is used, crystal glass is created.
Lead glass adds additional properties to those of regular glass. If more lead oxide is added, the melting point is lower and the glass is softer. Using a moderate percentage of lead oxide makes the lead glass more durable. Lead oxide slightly impacts visible light travelling through the glass. The refraction index is increased. The light bends and the light wavelengths are separated. These properties gives the glass a sparkly look.
The light refraction is not as apparent on window glass because crystal glass is typically cut in facets to increase the light refraction.
Lead glass is used in the nuclear power industry. When glass is infused with a higher volume of lead oxide, such as 65 per cent, the glass absorbs radiation and can be used as a radiation shield. As a comparison, a lead apron worn by an x-ray technician for protection has 0.25mm to 0.5mm of lead, while lead used in making windows has the equivalent of 1mm to 2mm or pure lead.
Lead glass cannot take quick changes in temperature or high temperatures. Lead glass used for food or drink leaches. For example, lead leached 89 micrograms into port wine after only two days of storage and after four months the lead level jumped to a range of 2,000 to 5,000 micrograms. White wine had an astounding jump in lead content. It doubled in one hour and then tripled in four hours. Other food items have similar issues such as jam stored in a crystal jam jar.
According to the Environmental Protection Agency, the allowed amount of lead consumption in water is 50 micrograms in a litre. Food and liquid can be served in lead glass but it should never be stored in lead glass or lead crystal.