FACTS ABOUT GLASS
One can make glass of a large number of subjects. Some elements may form glass themselves, but usually it is a compound of at least two substances. In most common glass, the base is sand and then they are usually called “silicate glass”.
Here in Stockholms Glassbruk we have a mixture of sand, soda and lime. The mixture itself is called “mäng”. The word comes from German gem = mixture.
The soda and the limestone are added to get a purer glass and to lower the melting temperature.
Glass melting furnaces can be divided into two main types: ovens and water ovens. The heating is mainly done with oil, gas, or electricity.
In a degel we have large vessel of refractory material. In the refractory vessel you put in the mäng. This means that the molten glass has no contact with the outer walled walls.
In a winnow (which we use here at Stockholms Glasbruk), we have constructed a large "bath" where we put in mäng. This means that instead of that of a degel, where a large vessel holds the glass in place, it will melt the glass all the way to the walled walls.
We have divided our winnow divided into two parts, a melting section and a working part. In the melting section we put in mäng and eventual uncoloured glass that we want to melt. (Glass that has color in itself we do not want to melt because it discolors the rest of the glass in the water). In the melting process, it varies between 1200-1300 degrees.
Once the glass is melted, we “fångar an”. To “fånga an” also comes from the German's word catch. The temperature of the glass while we fångar an is about 1200 degrees.
How long it takes to work with the glass before it becomes too cold to shape varies. What can play a role is how much you work with the glass, what tools you use and if you have stained the glass. If you want to continue working with the glass after that it has solidified, you can use an furnace. In a furnace there is no glass, but it is a sealed smaller oven that you only use to heat the glass, so that it becomes bendable and to moveable again. Heating in such an oven occurs with a gas oil flame and the temperature is around 1200 degrees.
To color glass there are two ways: either with crushed colored glass, which can look like anything from flour to larger crushed pieces, or with color bars of desired size.
To color glass add metal oxides. Some examples are:
- fluorine becomes white
- silver turns red
- cobalt becomes blue
- sulfur turns yellow
The tools we use have always looked the same. What we use most are cutting saws, plain wettened newspaper and a wooden ladle. (the ladle is made out of alder tree because it holds water so well). And a must is our pipes. The pipes are made of one meter metal pipes. At the end thereof, that receives contact with the glass during the process, there is a slightly thicker piece that has a more conical shape: that part of the pipe is called the navel.
When the glass is finished and solidified, it is still very hot, even though it looks cool. The temperature is usually at about 500 degrees when it's time to “knock off” (to remove the finished glass from the pipe) and then to set it in a refrigerator for it to cool. Even though it's called a “cooling oven”, it does not mean it's cold inside. In the refrigerator you want the same temperature as the glass is when you set it, which is around 500 degrees. A cooler like this is used to make the glass cool down more slowly. If you left the glass in the room after it was finished, it would be too big a difference between the room temperature and the glass of 500 degrees. Then there would be tension in the glass, which, ultimately, would cause it to burst.
Stockholms Glasbruk is renowned for its unique crackle-styled glass works. It is one of the oldest ways to decorate glass. Cracked glass is obtained by deliberately creating cracks in the glass’ surface. The hot glass (about 700 degrees) is dipped in water which gives a shock to the glass’ surface and creates cracks. The glass is reheated so much that it is only partly heated together, which creates a beautiful crackled texture.
Glass and the glass work’s road to Sweden
The oldest today preserved glass are as old as 1800 years before Christ. The Phoenicians learned the art from the Egyptians and developed the glass-blower, which became a like a revolution, enabling new forms and expressions. Over the centuries, the art of producing beautiful glassware and ornaments has wandered all the way from North Africa through Europe to eventually reach our remote Sweden.
From the second half of the 16th century there are traces of foreign champion’s glass manufacturing in Sweden. In 1641 the Swedish Melchior Jung became the first to build a glass mill in Stockholm. To the delight of the nobility and the rich bourgeoisie who were the only ones who could afford to enjoy the beauty of his glass. The common people probably had to cope with wooden mugs or, at best, mugs and glassed of tin.
Initially the furnaces were heated using wood, then oil and thereafter gas. Nowadays, we use electric and gas heater ovens.
The pipe has looked the same for about 2000 years. The frontmost part of the pipe is warm, and you have to roll the pipe constantly between your fingers to pick up the molten glass, otherwise it will fall down.