Is glass made by sand? If it is than why are there different types of Glass?

Most glass is about 70 – 72% silicon dioxide, or sand. There are at least three factors that make up what type of glass is developed. The first is determined by what materials are added into the mixture. For example, the most common type of glass is soda-lime glass which is nearly 30% sodium and calciium oxides. Pyrex is 10% boric oxide and lead glass is a minimum of 24% lead oxide. Additives can also be used to create tinted glass.

The second factor in the difference between different types of glass is annealing, or changing the rate of cooling. Regular glass is called annealed glass. Cooling the glass more quickly (heat strengthed glass which is about twice as strong as annealed glass) results in a stronger glass and glass that glass is even more rapidly cooled is called tempered glass, which is usually four times as strong as annealed glass.

The last item effecting the composition of the glass is the addition of coatings or laminates. Coatings, such as metal oxide coatings, are used to change the reflectivity of the glass, resulting in better energy efficiencies due to lower transmission rates. Laminates can be added to further strenghten the glass to produce burglar or bullet resistance or sound reduction properties.