Does anyone know how hot some glass, say a jam jar for example can get before it cracks?

glass varies in purity and composition. could you please specify?

Geometry (shape and thickness), as well as where and how heat is applied will have an influence.

it depends on how fast the glass crystals expand. If u have a more rounded jar it will have less tendency to crack, but if the jar has a flat bottom, the crystals will morph/expand at different rates causing the glass to crack. ALso, evenly heating glass can help prevent cracking.

Generally speaking, however, glass has no crystal structure. It is an amorphous solid and has no set melting point. Instead, it just softens and then melts. Now crystal glassware, however, does have a crystal structure and that will melt at a certain point and crack at a certain point. You're more in danger of glass cracking if you take it from a hot environment into a cold environment.

Does anyone know how hot some glass, say a jam jar for example can get before it cracks?

 

If you heat it slowly with hot air so that temperature difference will never exceed 50C in any part of jam jar then it does not crack, just starts to soften at 400C or maybe 500C. Common glass cracks if temperature difference between nearby points is at least 80C ... 120C. Temperature in itself does not count, just difference.

Thanks for the replies, I've found out what I needed to now

99,7 % SiO2

 

Density 2,2

Melting point 2300 °C (Go not above 1300 °C)

Same properties as Duran, Pyrex and Simax

 

Duran Pyrec Simax

 

Density 2,23

Melting point 530 °C (Go not above 500 °C)

Composition : 81 % Boron oxide, 4 % sodium-potassium, 2 % aluminium oxide

 

SBW

 

Density 2,45

Melting point 555 °C (Go not above 500 °C)

 

Ceran

 

Density 2,57

Melting point 700 °C (Go not above 700 °C)

 

Sodaglass, AR, Soda-potassium

 

Density +/_ 2,5

Melting point 300 °C (Go not above 300 °C)

Composition : 74 % silicium, 16 % soda, 9 % calcium carbonate and magnesium