Abstract: A method of prestressing at least one of the glass sheets of a sandwich safety glass, while being bent in a furnace, the glass sheet, after passing through a bending zone, being passed by a blow system and cooled by cooling air in the furnace in a temperature zone above the transformation point but below the deformation point of the glass, and an apparatus for such prestressing comprising a travelling die supporting superimposed sheets, a bending furnace zone to soften the sheets, and a cooling zone, the cooling zone having a blow system that subjects the bent sheet or sheets to cooling air.