Different chemical elements possess different ionic radius and therefore different densities.
Hence, if glass containing sodium is cooled slowly in a salt bath of molten potassium, the sodium ions will migrate from the glass to the salt, while the potassium ions will move to the surface of the glass where, due to their wider radius, they create a denser and therefore stronger surface layer (of no less than 0.1 mm).
Given the evolving phase of these sectors, the chemical tempering is suitable to find optimal arrangement between thickness and shape.
Today chemical tempering allows to obtain glasses previously curved and then chemically tempered also starting from thickness inferior to 2mm.
The shape of the glass sheet will not be modified during tempering.
Glass which has been chemically tempered is five to eight times stronger than the one which has not undergone any tempering process.