The medium burned by the Divine Fire is not matter, not sight, not sound, but perception!
No wonder they wanted two people to enter the final trial. With just one person, they might have used something like a sleeve to probe and foresee, but with two people who are competitors, the first foreknowledge will inevitably involve rushing up and fully contacting the Divine Fire, triggering this mechanism!
They could no longer escape the burning of the Divine Fire and could only watch helplessly as their skin became translucent. In an instant, they both transformed into glassy fire beings, and then—
As the last trace of Divine Fire converged within him, Ash turned to look at Silver Lamp and noticed that not only was her mask intact, but even her clothes were unscathed, which showed that the Divine Fire did not burn tangible objects.