The opal glass production on the test bench

The special features of opal glass

Opal glass, or cryolitho glass, as it is called in technical terms, is opaque glass, which creates a particularly soft light. This light is created by its translucent, white, milky glass. The opacity is achieved by tiny particles that are embedded in the glass. The even distribution of these tiny particles, which have a different refraction than the base glass, creates this special effect.

• The disadvantage of opal glass is its production, which is problematic for the environment. Manufacturers have to install special filter systems in order to keep the fluorine emissions generated during manufacture to a minimum.
• The lighting opal glass usually has three layers. Several steps are necessary for the production. There are 2 layers, the inner and outer, which are blown from clear glass and the middle one, which is mixed with cryolite. This creates the special color of the glass.
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• The difference to normal glass production is the addition of cryolite, a special opacifier. This is added to the glass base of the middle layer.

The manufacture of opal glass

1. First, the hot, tough glass is removed from a crystal glass vat. To do this, the glassmaker goes into the hot glass mass with a so-called glass pipe, approx. 2 - 3 cm deep. Now it is important to wrap the glass ball around the pipe navel in a specific twisting motion.


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2. Now the pipe is removed from the glass bath. In this way, the first gob of glass is separated from the glass bath. The result is a misshapen mass of glass that is placed on a rolling plate. Here it is smoothed symmetrically to the rotation of the pipe axis by even turning movements and simultaneous pressing against the plate. This avoids an uneven wall thickness.
3. Now air has to be blown into the glass mass. To do this, air is pressed into the pipe. Now the end of the pipe has to be closed with a finger. The air can now expand, but is prevented from escaping. This is how she shapes the soft glass.
4. The glassblower now blows in a little more air with his mouth, and the blank gains shape, then cools down quickly to around 600 degrees Celsius and solidifies. While it is cooling down, the glassblower carries the opal glass blank to the opal tub.
5. Here the glass blank is received by what is known as the transfer device. This pushes the Kölbel into the glass again. The greatest skill is required here.
6. The glass is wrapped around the crystal glass bulb with constant rotation. Even distribution is particularly important here. The pipe is now pulled out of the glass bath while turning quickly. At the same time, the glass thread is severed. Now a uniform, round structure is created from the glass mass. In this work step, the glass is subjected to a temperature difference of 840 degrees Celsius and turns white underneath.
7. The glass now comes back into the glass tub. Here it cools down again briefly and now comes back to the glassmaker. Depending on the specified glass shape, the appropriate amount of glass is now removed from the glass tub. This size varies between 2-15 kg. It is very important to pay close attention to the weight and the glass distribution of the flask. Otherwise this can affect the stability of the glass.

How the glass is shaped

1. To give the glass a shape, the goblet is placed in a wooden spoon provided for this purpose and is rolled in it. This is a technical term used in glass production that describes the special rolling in the wooden spoon. This gives the glass its later shape and is evened out.
2. This process happens within seconds and can therefore only be performed by very skilled workers.
3. Then the glass is placed in an iron mold and is blown into place here. Once the glass has cooled down and solidified again, the iron mold is opened and the pipe on which the glass is still attached is removed.
4. The separation that follows now takes place through a few drops of water that are dripped onto the joint between glass and metal. Tiny cracks form in the process. Then a light tap is enough to separate the pipe from the glass.