The main characteristics of glass are transparency, heat resistance, pressure, breakage, and chemical resistance. Glass is made of natural, raw materials, including sand, soda ash, and limestone that need to be heated at a very high temperature to melt and form glass.
Handblown glass is made by glassblowing and molded by hand, hence “hand” and “blown.”
The differences between handmade glass and handblown glass, are:
Cost – HG glass is 5-6 times more expensive to make, it’s also thinner and less “uniform” than machine-made glass.
Transparency – HG is more transparent and has a more refined finish, it can never be 100% duplicated
Inconsistency – HG is unique, it has an element of surprise, which lends to the of high cost and value of these items
The molten glass must be continuously and consistently heated before it reaches its final shape. Once the forming part is finished, the glass starts cooling down and must immediately start annealing. HG has to be properly annealed, otherwise, if it's not suitable for use.
Glass is annealed by placing it in a temperature-controlled chamber that allows it to cool slowly to
mitigate the internal stresses that are naturally present when glass is made. If the glass isn’t annealed or the process isn’t completed, the glass will have extreme thermal stress within, and if broken, it will often react like an explosion, even once it's cooled. This is what we see in tempered glass. This type of glass can break spontaneously at any point, and its unpredictable nature makes it extremely dangerous!
Another way of putting it is that lack of annealing makes glass weak and unreliable, which will lead it to crack or shatter when subjected to relatively small temperature changes or mechanical shock or stress.
If a glass artist is unsure whether glass has been annealed, they should always wear PPE, including gloves and goggles, when attempting to break it. Art Glass is another term used for Handblown Glass objects that are purely decorative.
Glass and resin artists who use reclaimed HG glass cullet or shards in their art should be aware that most of the salvaged glass is likely unannealed. One way to tell if the handblown glass has lost its structural integrity is to simply apply a little pressure to it, which will make it break and crumble easily. This glass is not good for further use unless you make glass frit from it.
Stress fractures in glass are often noticeable to the trained eye. If the glass looks cracked and it doesn’t reflect light, but instead diffuses it, the glass is not ideal for resin art. If you’re a glass fuser, you will notice that after the fusing cycle, this glass will look muddy and dull. Most glass artists to not "reuse" colored glass fragments, as it damages the "crucible," at the heart of glass blowing. The glass fragments are often "fritted" for glass fusing.
Annealed glass will break into shards, while tempered glass will break into smaller uniform cubed shapes, like shower doors and car windshields.
The inexpensive glass you find at Dollar Tree or other discount stores is more than often not annealed, especially heavy, faceted designs. The regular wine glasses and champagne flutes are safe to cut with a tile saw, or wet saw. Antique glass and Pyrex dishes aren’t annealed. You should always be prepared for glass to shatter when you cut it! Use necessary precautions.
Named for the Float Process that was invented by Sir Alastair Pilkington, float glass is manufactured by floating molten glass on a bed of molten metal of a low melting point. Window glass and other uniform clear glass panels used in construction, are types of float glass. It can clear or tinted.
The 4 main types of glass are:
Annealed Glass, which includes handblown glass that has no internal stresses
Heat Strengthened Glass, which is semi tempered
Tempered or Toughened Glass, which is hard to break