Glass

Glass is one of the earliest man-made materials. As early as 4000BC glass was used in the Middle East as decorative beads. A glass vase dating from 800BC is the earliest known example of clear glass. The most familiar form of glass is the Silica-based material. Glass is a biologically inactive material. When it breaks, it will break into sharp shards. The properties of glass can be modified or changed with the addition of other chemical compounds or the use of heat treatment. Glass is mostly found in household item such as light bulbs, windows, vase, and bottle. Aside from that, it is also used to make fibre optic cables and undersea cables. Glass that is used to make optical devices are categorised by a six-digit glass code, or alternatively by using a letter-number code from the Schott Glass catalogue.

• Borosilicate glass - used for heat-resistant cooking equipment like Pyrex
• Lead glass - for sparkling decorative glassware
• Glass fibre - for insulation and fibre optic cables

• Iron (II) oxide for a bluish-green colour (beer bottle)
• Chromium for richer green colour (wine bottle)
• Sulphur, carbon, iron salt for amber glass; from yellowish to black
• Boron, sulphur for blue colour
• Calcium for deep yellow colour
• Manganese for amethyst colour
• Selenium for reddish colour
• Selenium, cadmium sulfide for brilliant red colour
• Cobalt for yield blue glass
• Tin oxide, antimony, arsenic oxide for opaque white colour
• 2%-3% of copper oxide for turqoise colour
• Metallic copper to produce very dark red opaque glass
• Lead crystal, nickel for purplish colour
• Cadmium, sulphur for deep yellow colour
• Titanium for yellowish-brown colour
• Uranium for fluorescent yellow or green colour. (carcinogenic if grounded into powder)
• Silver for orange-red to yellow colour.
• Alumina for durability
• Boron to improve resistance to heat or cold

Whilst most glass containers are recyclable, this symbol will allow consumers to identify the glass that could be recycled more accurately.