Types of Glass

Mario Moretti

Glass also exists in a natural state. The most common one is obsidian, a dark shiny material, which is very hard, formed in volcanic rocks and which man learnt to produce to make objects (blades, arrow-heads, etc.) over one million years ago.

Tektites are small glassy pebbles formed from the impact of meteorites on the earth's surface. All that's needed is sudden lightning on a beach to transform silica into threads or blocks of glass, called fulgurites.

Of all the artificial materials, glass is one of the most used and certainly the most versatile, with so many unique properties (easy to shape, transparent, long-lasting, cheap), which, in many applications, it will be difficult to replace with other materials.

There are numerous types of glass that can be classified in different ways on the basis of:
- the production technique (blown, pressed, moulded...);
- the use (for pharmaceutical and food use, construction, eyewear...);
- appearance (coloured, uncoloured, transparent, opaque...);
- particular properties (neutral, biocompatible, athermic...);
- chemical resistance (inert, long-lasting, not long lasting, soluble...);
- chemical composition (quartz, calcic-sodium-silicone, boron-silicate, lead...).

Glass can be used alone or with other materials (metal enamels, ceramic windows...).

What follows is a description of the main composition categories.

I. Molten Quartz

Molten quartz (silica glass) is an ideal vitreous substance due to its chemical and physical characteristics, but production costs are high due to the difficulty of its fusion at high …

II. Sodium Silicate

Sodium silicate (soluble glass) is a transparent product, easily soluble in water, which is used widely in many industries. The greatest quantity is used as dishwashing detergents but it is …

III. Calcic-Sodium-Silicone

The calcic-sodium-silicone glass (common glass) group is the one most commonly used in glass work production, for sheets for construction, furnishings and vehicles, bottles, table glass …

IV. Borosilicate glass

This is glass with a high chemical resistance (this is why it is called neutral) and a highly varied composition: it generally contains relatively high quantities of alumina (Al2O3) and …

V. Lead glass

This term applies to transparent glass that, because of its high quality, looks like natural rock crystal. Particularly pure glass with a quantity of lead oxide over 24% is part of this …

VI. Eyewear glass

It is the most precious glass; its composition is highly varied to achieve the many relationships between the necessary refraction and dispersion. Some eyewear glass types include: flint …

VII. Special glass

There is no end to glass with different compositions, used for particular applications like alumina-silicate glass (fibreglass, objects to be submitted to chemical tempering), phosphate …

VIII. Glazes or Enamels

Lastly, glass of different compositions is used as a thin layer applied by firing as a covering of other materials like metals (enamels) or ceramic bodies (glazes or enamels). They are …