Air burn is a localized scorched or discolored mark created when trapped gas is compressed rapidly between the sheet and tool. The temperature rise occurs in a pocket that has no effective escape path. It should not be confused with radiant heater scorching, which follows the oven pattern rather than the final sealing geometry.
The mark usually appears at the last point of contact in a deep or closed feature. High forming speed, pressure applied before adequate venting, blocked passages, and an overly smooth sealed surface increase the risk.
Correction
The affected pocket should be given a reliable evacuation route. Vent position, connected channel, valve sequence, and pressure ramp should be reviewed together. Slowing the initial pressure application may help diagnose the mechanism, but the final process still needs enough speed to form the sheet before cooling.
The tool face should be inspected for contamination because a burned deposit can reproduce the mark after the airflow issue has been corrected. Heater settings should not be reduced unless sheet-temperature evidence shows that radiant overheating also exists.