What is glass and how is it produced?
Glass is a hard material normally fragile and transparent common in our daily life. It is composed mainly of sand (silicates, SiO2) and an alkali.
These materials at high temperature (i.e. molten viscous state) fuse together; then they are cooled rapidly forming a rigid structure, however not having enough time to form a crystalline regular structure.
Depending on the final use and application the composition of the glass and cooling rate will vary to achieve the adequate properties for the specific application. These are the common ingredients to obtain glass and back painted glass:
1. Sand (SiO2 silica)
In its pure form it exists as a polymer, (SiO2)n.
2. Soda ash (sodium carbonate Na2CO3)
Normally SiO2 softens up to 2000°C, where it starts to degrade (at 1713°C most of the molecules can already move freely). Adding soda will lower the melting point to 1000°C making it more manageable.
3. Limestone (calcium carbonate or CaCo3) or dolomite (MgCO3)
Also known as lime, calcium carbonate is found naturally as limestone, marble, or chalk.
The soda makes the glass water-soluble, soft and not very durable. Therefore lime is added increasing the hardness and chemical durability and providing insolubility of the materials.
Other materials and oxides can be added to increase properties (tinting, durability, etc.), produce different effects, colors, etc.