Glassware is considered "oven safe" based on its ability to withstand changes in temperature without shattering or breaking. While it's true that glass is typically made at very high temperatures (around 1700°C or 3092°F) and begins to melt at about half that temperature, the temperature range that glass can tolerate without significant damage is narrower than the extremes it experiences during its manufacturing process.
The thermal shock resistance of glass is an important factor to consider when determining if it's safe for use in the oven. Thermal shock occurs when there is a rapid and significant temperature change in a material, causing it to expand or contract unevenly, potentially leading to cracks or breakage. Glass with lower thermal shock resistance may not be able to withstand sudden changes in temperature, such as moving from a hot oven to a cold surface, and could shatter as a result.
Glassware that is labeled as "oven safe" is usually specially treated or made from tempered glass, which undergoes a controlled thermal process to increase its strength and thermal shock resistance. This treatment makes it more resilient and capable of withstanding the temperature fluctuations typically encountered in ovens.
On the other hand, glassware not designated as "oven safe" may lack the necessary properties to handle the stress of oven use and may be prone to breaking or shattering when exposed to high temperatures. Using non-oven-safe glassware in the oven can be dangerous and should be avoided to prevent potential accidents.
In summary, while glass is made at very high temperatures, its ability to withstand temperature fluctuations and thermal shock varies depending on its composition and treatment. Only glassware specifically designed and tested to be oven safe should be used for cooking or baking in the oven to ensure safety and avoid breakage. Always check the manufacturer's recommendations for temperature limits and oven use before placing glassware in the oven.