Difference between Glass and Crystal: What are they? How are they processed?
To distinguish a glass object from a crystal object, a careful eye may be needed. In fact, the crystal is very similar to glass, but has particular peculiarities of shine, transparency, elasticity and sound.
Characteristics that make it much more precious than glass, despite being similar to the appearance. But it is in depth that the differences lie: the presence of lead in the chemical structure of the crystal, in fact, plays a fundamental role.
Tuscany is one of the major producers and exporters of crystal, thanks to the perpetuation of the ancient and difficult art of glassmaking that has now become a profitable economic activity, one of the few sectors that also offers work to young people. Just think that in Colle Val d'Elsa, which is called the 'Italian Bohemia', 14 percent of the world’s crystal is produced and 95 percent of the Italian one.
In this article we will see what differences characterize these two materials, we will understand how they are worked and how they are produced.
Definition and characteristics of glass?
The process of creating glass is obtained by melting a silicate mixture at high temperatures, and then having it cool down. Among these we find quartz and other chemical substances, including boric anhydride and phosphoric anhydride, called precisely "Vitrifying substances".
The material thus obtained serves to manufacture windows, glasses, vases, chandeliers and many other objects.
Glass is a homogeneous material with a random, non-crystalline molecular structure (similar to liquids).
The manufacturing process requires that the raw materials are heated to a temperature sufficient to produce a heap of completely molten material. It, if cooled quickly, becomes rigid without crystallizing.
If we consider the three classical states of matter (liquid and gaseous solid), glass is like a fourth state of matter that combines the rigidity of the solid with the molecular structure of liquids. It is often described as a Glassy state.
The glass can be melted again and reused countless times and this is why it is pushed for separate collection.
Many countries use the "return vacuum" mode to retrieve used bottles and return them to the market at minimal cost.
Definition and characteristics of the crystal?
Crystal is a glass that has certain characteristics of shine, transparency, elasticity and sound. These qualities are provided by the presence of lead oxide.
Thanks to lead, in fact, the crystal is brighter, because it has a greater refraction and the touch is more sonorous than glass.
This also increases the strength of the material, allowing to manufacture objects much thinner than glass, but also more delicate. In particular, a glass becomes crystal only if it contains at least 24% lead.
The name "crystal" comes from the fact that it has a reticular structure, called "crystalline lattice", formed by atoms and molecules arranged in an orderly and regular manner.
Contrary to what intuition suggests, it is a relatively soft material. Moreover, the brilliance that characterizes it, due to the refractive index, can be accentuated with cutting and engraving techniques.
It is slightly more expensive than calcium sodium glass and is preferred for use in the electric field due to its excellent insulating properties.
The tubes for thermometers and the artistic are made of lead and alkali glass, commonly called lead glass.
This type is not resistant to high temperatures or sudden thermal changes.
How is the crystal worked?
As already mentioned, the base is transparent crystal glass in which the calcium components of ordinary glass are replaced with lead oxide (pbo).
Crystal typically contains 18-35% lead (pbo). Lead oxide adds a higher density, lower heat conductivity and higher refractive index (and therefore higher gloss) to the glass. In addition to this, there is also greater resistance (products containing lead oxide weigh more), although they are at the same time more delicate.
Different additives (metal oxides) are used to obtain a coloured crystal. Thanks to this addition, you can get crystals ranging from ruby red to violet blue, even amber.
In this process you will get the finished product, which is created by combining the transparent crystal layer with a layer of colored one.
At this point, therefore, the glassmaker blows the material at a temperature of about 800 inches C. The final shape will then be obtained by pouring the still liquid crystal in a form of wet beech wood in which the master glassmaker will blow for the last time.
Differences between glass and crystal
Needless to say, the main difference between glass and crystal is the presence of lead oxide. This gives the glass some characteristics that make it particularly interesting.
Lead, in fact, causes the density of the glass and therefore the refractive index to increase considerably. In this way the glass is close to the optical properties of diamond: the light that hits it is refracted in a more decisive way than with normal glass, thus giving the effect of great brilliance typical of lead glass.
The greater the lead oxide content, the more glass containing at least 24% by weight is allowed to be called crystals or "Crystal Glass".
Such a high addition of lead oxide, or even higher, would give a yellowish hue to the glass. It is only the wise correction in the composition of Glass made by chemists specialized in concert with master glassmakers that make the Lead Glass clear, transparent, brilliant, stable, worthy of being called Crystal.
In order to be easily recognized, all European countries have created an important EEC standard (69/493) that characterizes with its own labelling different types of glass according to composition, refractive index and specific weight.
For centuries, the production of glass and crystal has been a resource for Tuscany. At Amarzo, with our production of 100% recycled glass design products, we share in this extraordinary tradition. Come and discover the products on our Site.
Article edited by Renato Sarlo