People have been making glass for thousands of years. It can occur naturally where extreme temperatures melt silica (or silicon dioxide, also known as quartz) in sand, so it is not terribly complicated to replicate; just add heat and sand.
Glass can be used for dozens of applications from microchips to containers, lenses, art, insulation or building material. No matter how you use it, you generally have to melt it down and homogenized to get it into the shape or structure you want.
Pure quartz starts to melt at approximately 1,650 degrees Celsius (3,000 degrees Fahrenheit) and turns into actual workable glass at 2,300 degrees Celsius (4,172 degrees Fahrenheit). In this form quartz glass has a narrow temperature window in which it can be manipulated. This is why pure crystal in any form (from art to drinking glasses) is generally more valuable than standard glass; it is thermally stable and physically tough. Common glass is usually characterized by the adding of compounds to lower melting temperatures and increase the window of temperatures in which the product can be manipulated. This comes at the cost of physical and thermal stability, and often at the cost of clarity as well. Often added is sodium carbonate (soda) to lower the melting point and workable temperature of silica to 1,500 degrees Celsius (2,732 Fahrenheit).
Often present in sand is elements of iron (among other imperfections depending where you are getting sand from), which add a green tint to glass. This is why old glass often features a green tint and breaks easier.
You can melt glass using a furnace or a kiln with charcoal or gas, or specialized electric melters. You will need something to melt the glass in to contain it, this is called a “crucible“. It can be made of anything which exceeds the melting temperatures of glass; often ceramic and even graphite. From the crucible it can be homogenized (by stirring with a stir rod in order to standardize all compounds within) and poured into molds or handled with instruments to manipulate it into shapes and structures. Use crucible tongs to handle the crucible along with furnace gloves and protective eye-wear at all times. Also be sure to wear a face mask while handling silica powder so that you do not inhale it.
Molten glass in any of its forms is extremely dangerous if not handled properly and cautiously, as is operating any form of furnace or kiln. Again, wear protective eye-wear, clothing and heavy gloves; the more heat-resistant the better.
Quartz silica will melt down much easier if ground down first. You can use a mortar and pestle. The smaller the particles the easier and more consistent the glass will melt. You can even break down glass and melt it again, or grind recycled glass into sand if you don’t have enough. Once your glass is in molten liquid you can do anything with it from making windows to decorations. Just make sure you have a game plan in place before melting, you won’t have time to stumble around and set up a mold.
We also have introductions to working glass:
- Using Glass Molds
- Blowing Glass
- Making Glass Window Panes