If it can be used in an oven, what does "heat-resistant temperature difference of 120℃" mean?

The 120℃ standard does not represent the absolute maximum temperature the dish can endure, but the range of sudden temperature change. The heat-resistant temperature difference of IWAKI glass is 120℃, which means the temperature difference it can withstand without damage when rapidly cooled by pouring water over heated glass^[1]. Because this limit is different from the ability to withstand high temperatures itself, it can be used without problems even in home ovens reaching about 300 to 350℃^[2].

The main cause of glass breaking is not high heat itself, but the impact caused by uneven contraction between the exterior and interior due to rapid temperature changes. Therefore, if you pour cold water on it immediately after cooking in the oven or place it on a wet dishcloth, the instantaneous temperature difference may exceed 120℃, potentially causing the glass to break. Immediately after taking it out of the oven, it is safe to use a dry trivet and let the dish cool naturally.