Abstract: Apparatus for treating fragile vitreous articles such as glass sheets which are apt to break when the treatment involves thermal conditioning. The apparatus includes spaced conveyor members for conveying the articles in a predetermined direction over a treatment area. To assist in the easy removal of any broken fragments of said vitreous articles, the treatment area is located beneath the conveyor members and has a plurality of heads for treating the underside of the articles. The treatment heads are retractable from a treating position, where they project into the spaces between the conveyor members, into a retracted position, where they are spaced beneath the conveyor members. A sweepable fragment collecting surface is spaced beneath said conveyor members. A sweeper is provided for cleaning the collecting surface when the treatment heads are retracted.