Technologies

The company Crystal BOHEMIA manufactures a wide variety of quality crystal products. Each product is subject to stringent health safety requirements, which is proven by certificates issued by appropriate institute. 

The company respects the environment. Because of the development of the town, our glassworks, formerly built in middle of the fields, has ended up in its centre.  Therefore, all our safety and protective standards are more demanding than respective regulations imposed by the EU.

 Glass material 

The basic material for lead crystal production is glass-making silica sand. For our needs, we use solely the sand from the deposit by the village Střeleč nearby the town Jičín in Eastern Bohemia. So called batch contains not only sand, but also other raw-materials, which are weighed out in fixed rate according to the technological order, and thoroughly mixed. They include mainly potassium carbonate (potash), sodium carbonate (calcined soda ash), potassium nitrate (saltpetre) and other substances, e.g. refining agents.

 What is substantial for lead crystal, what causes its unique appearance and possibility of further processing, is the lead monoxide (litharge). Our glass contains at least 24% of it, which is the highest ratio in Czech countries.

 Usually, one half of the charge volume (batch inserted to the furnace) consists of cullet (crushed glass fragments). Cullet serves for better melt-through; its chemical composition must be identical with the composition of melted glass. Glass is melted at the temperature of 1440 °C, in continuous tank furnaces heated by natural gas.

 

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Forming

 Crystal BOHEMIA employs recent automated technologies if possible. Their productivity, possibilities and extraordinary precision form the base for production of high quality products at affordable prices. Despite the fact that automation made a considerable progress, some partial manufacturing operations cannot be perfectly replaced by machine work, therefore there is still a need of handwork as well.

 Glass is formed in cast-iron or steel moulds at the temperature of about 800 °C, using blowing or pressing. This variability enables us to utilize benefits of both these manufacturing methods and to offer different types of articles to our customers.

 Before or just after taking out the pressing from the mould, its sharp edges are melted by flame of a gas burner. The product is then cooled a bit just at place to avoid its deformation. After a very short time, it is carried to a conveyor belt lehr and it is annealed gradually. The annealing (cooling) time depends on glass thickness and product size; the thicker or bigger one is to be annealed for longer time. This very important process avoids spontaneous cracking of glass as a result of internal stress.

When annealed, it is necessary to remove useless parts, so called caps, from blown and also from some pressed semi-products. Using cracking-off machines, a sharp flame of gas burner is used for rotational shapes; for non-rotational pieces, removing is done by manual notching, using grinding wheels or diamonds. Afterwards, sharp and uneven rims are levelled by grinding, or by flame burning in case of stemware. Matt surfaces of the products that remain after grinding or burning-off are chemically polished using special polishing devices, where a mixture of sulphuric and hydrofluoric acids is applied.

 

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Cutting

Typical characteristics of lead crystal – its pureness and high index of light refraction – become really apparent in case the product is adorned by cutting. Only then a beautiful play of lights and shades on edges, cuts, or facets of the cut decoration can be admired.

 Lead crystal is probably the most beautiful type of glass at all. To show off its unique properties as much as possible, Crystal BOHEMIA employs the original way of decorating, i.e. manual cutting. In this way, it follows centuries old skills of Bohemian masters of the art of glassmaking.

On a product, a basic plan for future pattern is sketched with colour before cutting. Cutter receives a drawing and follows it strictly. For glass cutting, diamond or corundum disc is used. Each, even the smallest cut represents one or more approaches of the product to a quickly rotating disc. The work of a cutter needs both artistic feeling and handiness, but it can be also really strenuous and hard work - some pieces (e.g. bowls and vases) weigh up to 20 kilograms.

 Our company provides our customers also with other ways of decorating (colour spraying, metal-plating etc.)

Crystal Bohemia, a.s., Jiráskova 223/19, 290 01 Poděbrady

Phone: +420 739 488 911 |  e-mail: company@crystal-bohemia.com