DIY glass etching, enameling, how to make glass and more...

The glass therefore always consists of a mixture of a very large number of silicates. This explains why the molten glass does not crystallize on cooling and remains glassy. We must assume that the different compounds greatly slow down the crystallization rate on both sides. We can clearly see that this tendency to crystallize still exists when a large quantity of glass is poured into a block at a glass factory and can therefore only cool down very slowly. Here, after a few weeks, only crystallized material can be found and therefore no more glass. Every glass blower knows the phenomenon that when old glass tube is processed for the blowing flame, the tendency to crystallize is great and it is often not even possible to bend an old glass tube.

We must therefore regard glass as a supercooled liquid, the toughness of which has become so great that it gives the impression of a solid. When we keep glass for a long time just at the temperature where it softens, a large number of small crystals form, the glass becomes opaque, it deglazes and it now looks like porcelain. By pressing this devitrified glass into tiles, a very beautiful wall covering is obtained.

Suddenly dipping the hot glass into hot oil causes the glass to become extremely hard; this glass does not break easily, however, from a scratch it can suddenly shatter into a large number of small pieces, just like the well-known glass tears, which are obtained by dropping a drop of molten glass into water.

By adding the different metal oxides it is possible to vary the properties of glass to infinity and it is therefore always possible to find a type of glass that is most suitable for a certain purpose.

A special type of glass is the enamel, which is used to cover metal or pottery. Enamel usually consists of an easily fusible lead-boric acid glass that is made opaque with insoluble compounds. In ancient Byzantium, later in China and Japan, and also in Europe in the Middle Ages, enamel was used to make very beautiful works of art, preferably by covering precious metals in a pattern with differently colored enamels. The colors are separated from each other by soldered edges of metal (émail cloisonné) or recessed places are engraved in the metal and filled with enamel (émail champlevé). To make enameled iron, which is used today for so many household items, one must first apply a layer of ground enamel to the iron, which adheres well to the iron and does not react with it.

Finally, by further developing the technique of melting at very high temperatures, it has also been possible to fuse the components of many precious stones together and to crystallize them on cooling. These real synthetic gemstones, which therefore have exactly the same composition as the real stones, are practically indistinguishable from them. The best-known artificial gemstone is the ruby, which is made by blowing a fine powder consisting of pure aluminum oxide and 2% chromium oxide through a firecracker flame onto a pin of refractory mass. The powder melts and solidifies on the refractory pin, immediately forming a crystal that continues to grow due to the newly added molten powder. Finally, a crystal has thus been obtained which often shatters on cooling and can be ground into decorative stones.

The mixture is now melted, and as quickly as possible, as certain components, which make the enamel opaque, should not come into contact with the hot melt for too long.

To speed up the melting, alkalis such as borax are usually added, which melt very slowly and then either dissolve or chemically attack the other ingredients. So one melts until the mass is sufficiently homogeneous and has not formed into a transparent glass. In this case, the mass as enamel is unusable.

The molten mass is now allowed to cool and the glass is ground to certain finenesses. Again, care must be taken here. The fineness depends on the way in which the enamel is applied later. Certain types of enamel must remain fairly coarse, while others are ground considerably finer.

The coatings are applied in the same way. In general, enamel layers are kept as thin as possible, but so thick that they cover sufficiently.

The drying must now take place very quickly, but not too quickly, as small cracks will then appear. Especially when the enamel paste contains salts, the risk of rusting is very high and the rust stains cannot be made to disappear again. In addition, white enamel in particular must be dried as quickly as possible, as when wet, dust from the air easily adheres and causes dark dots.

The objects must be placed very accurately in the drying oven. The air circulation must be good so that no drops of condensed water run over the enamel and cause streaks. The dried objects must now be handled very carefully, as any impact may cause the enamel to come loose. However, the error only appears after burning.

The burning of small objects and white enamel takes place in muffle furnaces, the burning of large objects and dark enamel in open flame furnaces. The objects are placed on the sharpest possible iron points of a grid, so that the enamel comes into contact with the iron with the smallest possible spots. A kiln is filled with objects of as uniform size and thickness as possible, since the duration of the burning differs too much. The quality of the enamel depends very much on the filling of the ovens. Thick metal parts not only burn much more slowly themselves, but also absorb the heat from the immediate surroundings. A thin object that has been standing near this may have remained too cold and therefore not cooked.

The burning temperature depends entirely on the composition of the enamel and is tested in a small test for new types of enamel. muffle furnace determined.