Heat Soaking is a quality contol check carried out, when specified, to detect and reject any toughened glass that may have inclusions (Nickel Sulphate) or edge defects that may cause breakage after installation.

Shipa Heat Soaked Glass can be used in citical aplication areas to minimize (if not totally eliminate) the risk of spontaneous breakage.

Nickel Sulphate (NiS) has been known to be the cause of spntaneous burst in tempered glass. During tempering the nickel sulphide is transformed to the high tempered α- phase (t>380C) has no time to retun to the β- phase on quenching. With the passage of ime NiS slowly inverts to the low temperature β- phase with the increase in volume of bout 4%. This volume expansion may cause glass breakage.

The heat soak is a destructive treatment which heat the glass for several hours at about 290 C to speed up the α -NiS to β - NiS transformation and consequently forces the contaminated glassess broken within the oven.