Glass and candle making--heat resistant is best.
Glassware is one of the most used mediums for container candles. Glass is easy to find and use in candle making. Beer and wine bottles have become popular to use as recycled candles. I would advise candle makers to shy away from these projects for safety and liability reasons. While all glass can break under high heat situations heat resistant tempered glass is made to better withstand the stress. From what I understand beer and wine bottles are not made from heat resistant tempered glass and will not withstand a quick change in temperature. They may be pretty but they can be pretty dangerous as the glass is more likely to shatter.
"When most materials are heated, they expand; when cooled, they contract. This property is known as thermal expansion, and the number which designates how much a given material expands or contracts is called its thermal expansion coefficient. Glass has a high thermal expansion coefficient, which means that it expands very rapidly when heated. This rapid expansion can cause the glass to shatter, a consequence known as thermal shock. Glass can be made to resist thermal shock by changing its chemical composition, method of manufacture, or both." (WiseGeek) In other words, when the candle gets hot or the flame gets close to the side of a container it can more easily shatter a non-tempered glass.
Only heat resistant glass should be used. Look for glassware specially made for candle making, lab equipment, hot food preparation or canning. And use caution in re-using candle glassware. Any chips or scratches may affect the integrity of the glass. Also, glass is technically a liquid (you can see wavy lines in old barn glass) and the more that a glass jar is used the more stress that it undergoes and will become brittle with age.
Lastly, if you want to use wine or beer bottles I would check with your insurance company to see if this type of glass would be covered for candle making. It's something to think about.
For some examples of tempered glass view our website.
"When most materials are heated, they expand; when cooled, they contract. This property is known as thermal expansion, and the number which designates how much a given material expands or contracts is called its thermal expansion coefficient. Glass has a high thermal expansion coefficient, which means that it expands very rapidly when heated. This rapid expansion can cause the glass to shatter, a consequence known as thermal shock. Glass can be made to resist thermal shock by changing its chemical composition, method of manufacture, or both." (WiseGeek) In other words, when the candle gets hot or the flame gets close to the side of a container it can more easily shatter a non-tempered glass.
Only heat resistant glass should be used. Look for glassware specially made for candle making, lab equipment, hot food preparation or canning. And use caution in re-using candle glassware. Any chips or scratches may affect the integrity of the glass. Also, glass is technically a liquid (you can see wavy lines in old barn glass) and the more that a glass jar is used the more stress that it undergoes and will become brittle with age.
For some examples of tempered glass view our website.