The magic of glass
Crystal objects look similar to those made in glass, both are achieved through a long process of melting and re melting. The glassy state is obtained by the cooling of various components that were previously in liquid state. Common components which are able to resist the glassy state are: silica, boric oxide and the phosphoric anhydride, which, because of this property are known as "vitrifying" components. Glassware will certainly not be formed only by these components, although clearly their measure will be predominant. A glass compound for example from silica alone would be very difficult to achieve, as apart from having ovens capable of reaching extremely high temperature to melt the silica (at least 1700 ° C), it would be very difficult to model.
In the manufacture of common glass other appropriate substances are added to the silica, in particular sodium and potassium compounds, which have the ability of lowering the required temperature of fusion of the silicie and thus to obtain a liquid mass processable at a lower temperature and therefore more easily manageable, these are known as melting substances.
Watch the informative video on the glass.
However, by only adding sodium and potassium to the silica, we obtain an unstable vitreous material, which is even soluble in water, and therefore vulnerable to atmospheric agents. From here we now need to add substances called stabilizers, which allow us to overcome the previous drawback. Lastly we add a substance which refines and homogenises the melted mass to perfection making it more "pure".
When does glass becomes crystal? The substantial difference between glass and crystal is given by the presence of lead oxide. The presence of this component gives the glass a few features that make it especially interesting. The PbO, in fact, means that the density of glass itself and hence the refractive index increases in a remarkable way. In this way, the glass provides a close fit to the optical properties of diamond: the light that hits the crystal is refracted much more than normal common glass, therefore giving a beautiful typical large brilliance of lead glass. The effect will be greater the higher the percentage of this oxide Lead.
Only glass which contains at least 24% of PbO by weight can by law be called CRYSTAL Glass or Crystal. Such a high addition of Lead Oxide, or even more than 24% of lead would give a yellowish hue to the Crystal. Only the wise correction in the composition of glass made by chemists specialised in glass can make clear lead glass, transparent, brilliant, stable, worthy of being called CRYSTAL.