About Glassblowing
At Ojinika Glass we do a style of glassblowing called Flameworking or Lampworking. The torch is fueled by a combination of propane and oxygen. Using a flame means that we can heat specific parts of the glass that we want to move instead of the entire piece at once, which allows us to do fine detail. We are limited with the size of the pieces we can make which is dependent on the size of our torch/flame.
All Ojinika Glass products are handblown and flameworked using top quality borosolicate glass.
Borosilicate (hard) glass is a type of tempered glass known for it durability and ability to resist thermal shock. The common name for it is Pyrex. It has a COE (coefficient of expansion) of 33.
It is mainly used in kitchen cookware and scientific laboratory glassware. It is considered "unbreakable" compared to the common soft/soda-lime glass.
The colours in glass are created from a combination of metals. Compounds like cobalt make up blues and cadmium makes red. Some types of glass change colours depending on the type of flame you use them with (oxidizing or reducing) - those are called polychromatics. There are also some types of glass that are UV reactive. 
To maximise strength, each piece is annealed in a kiln after being shaped in the torch flame. This process smooths out stresses and locks the molecules in place to increase durability. .
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You can learn more about the science of borosilicate glass HERE:
https://www.sciencedirect.com/topics/chemistry/borosilicate-glass