Theory 146/Glass tempering/Threshold lens
Tempering Needs a Thickness Floor
The claim
Tempering fails below a threshold in thickness, because the temperature gradient cannot develop across a thin sheet.
01Mechanism
Stress requires a gradient; below the threshold the whole sheet cools nearly uniformly.
02Prediction
Tempering should fail below a thickness.
03Refutation
Tempering tracking cooling rate alone would remove thickness.