Chemical and physical data

!!! Our glass is leadless !!!

Glass batch for melting our coloured glass has the same chemical base  – except colours No. 200, 207, 221, 222, 223,OP,OP-M,OP-U.  Apart from these, all our colours are fully compatible and they can be mixed (fused to alloys). In case of mixing colours I recommend to read through article (see below): Risk of mixing colours.

We deliver glass standardly in cast blocks. Blocks contain bubbles which follows from the processing technology.

LEADLESS  MOLTEN GLASS  1 meltage cca 250 kg, larger amount after agreement
CAST BLOCKS  20x20x2.5 cm, cca 2.5 kg +/- 2%
MELTING TEMPERATURE  820 – 860 °C
TOP COOLING TEMPERATURE  475 °C
DEFORMATION POINT  545 °C
THERMAL DILATATION=COE  α 20-300 °C 10 ˙ 10-6 K = 10
SPECIFIC WEIGHT  2,5 kg/l

The initial digit in the colour number indicates the group of related colours:

1 . .   crystals (various shades)

2 . .   yellow, topas, amber

3 . .    blue, violet

4 . .    aquamarine

5 . .    green

6 . .    alexandrites, rose, red

7 . .    combinations of coloured grays (deep toned colours)

8 . .    uranium glass (coloured glass with green ultraviolet effect) – harmless to health

OP     hazed white and coloured molten glass

 

Uranium glass

Glass with  added uranium reacs to ultraviolet component of radiation (sunshine, some halogen bulbs, ultraviolet lamps, fluorescent tubes etc.) and the ultraviolet component thus generates a green reflection effect.

According to the directive of SÚJB (Státní úřad jaderné bezpečnosti, State Authority For Nuclear Safety) glass containing less than 1 % of uranium is not considered radioactive.  Such glass does not emit measurable amount of radioactivity  and it is harmless in the sense of any exposition.  

 

Risk of mixing colours

 

As the technology of production of large glass objects is being developed, large demand arises to combine two or more pieces of glass. The practice of recent years proves that this can be done using glass materials with precise dilatation. Our glass meets these requirements; however, it needs to be said that:

  • we do not guarantee use of multiple colours in one object of kiln casting; even though we observe the production technology of our glass with utmost care, use of multiple colours in one object is risky
  • the large and thicker the glass object, the more tension remains in the glass (glass is a toughened melt and the tension can never be completely removed from it during cooling)
  • during passage of thermal rays through the glass object the light is filtered to various components which have different thermal character and therefore they can warm up the object irregularly – obviously due to low thermal conductivity of the glass this is happening especially on the surface of the glass object, however this causes the risk of excessive tension inside the object
  • in order to reduce the risk it is necessary to perform dilatation test on a small sample prior to production of large glass object, i.e. to cast the glass materials, properly cool them and check joints of individual colours under polarization scanner – this will minimize the risk of using incompatible glass materials

Conclusion: many artists are successfully using multicoloured production of glass objects from our materials and they are able to explain to the customers where the object can be placed so as to minimize the risk of tension due to external effects.

In order to reduce these risks we are developing new glass materials. In 2012 we have managed a small miracle and we have developed :  a specific low-dilatable glass EX, which can be used outdoors.