What is Hard Glass

Hard glass has a high viscosity at high temperatures.

Its softening point is also high, which makes it a bit difficult to melt.  

This type of glass is also known as borosilicate glass.  

It is made up of mainly boron oxide and silica.

This type of glass is less dense then soft glass known as soda-lime glass.  

It also has low coefficients for thermal expansion that makes it more resistant to thermal shock compared other commonly known types of glass.  

In fact, this glass has around one third of the thermal expansion coefficient than normal glass does.

This glass has a COE of 32 for comparison the Spectrum System 96 glass has a COE of 96.

This fact makes this glass more durable, because is heat and chemical resistant.  

This makes this type of glass ideal for telescope mirrors, laboratory chemical equipment and other places where it is imperative for the glass objects to retain their shape.  

It can even be used to process radioactive waste, as this waste is immobilized in a glass container using the vitrification process.

This glass is so heat resistant that the Space Shuttle's tiles have a coating of Borosilicate glass or hard glass on them.  

During re-entry, the tiles protect the shuttle for burning up in the atmosphere.  

Other uses for this glass include glass blowing and kiln projects for jewelry and other artistic projects.  

The borosilicate glass is used is beverage and other glassware, as it is dishwasher and microwave safe.

Brief History of Borosilicate Glass

Otto Schott, a German glassmaker, developed borosilicate glass during the latter part of the 19th century and marketed under the Duran brand name during 1893.  

The Corning Glass redid the company's operations and brought out Pyrex glass in 1915.  

From then on, Pyrex has been synonymous with borosilicate glass at least in English-speaking countries.

The Importance of Using the Same COE Glass

Since all the different types of glass used in glass fusing projects vary in COE, it is important for you to make sure you use like glass in all your projects. 

You do not want to mix a 30 COE glass with a 96 COE glass. 

This would cause the project from turning out as desired. 

Your project could wind up cracking where the different glass meets instead of fusing together properly. 

To prevent this always make sure that all your glass in a project is compatible according to their COE for this reason.

Different glass could also have different temperature needs, because of the varying COEs. 

This could keep your creation from being successfully fired in the kiln. 

To make sure that all pieces of your glass melt in unison, make sure their COEs are compatible.

Remember when working with hard glass to mix it only with other pieces of it.  

In this manner, you will be assured of your project turning out a success.  

Learn what each type of glass needs in the kiln for successful glass fusing results.  

It is a fascinating art form when done in the proper manner with the correct knowledge.

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Technical Terms

Hard Glass to Glass Fusing Made Easy

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