Glazing, which derives from the Middle English for ‘glass’, is a part of a wall or window, made of glass. Glazing also describes the work done by a professional “glazier”. Glazing is also (less commonly) used to describe the insertion of ophthalmic lenses into an eyeglass frame. Common types of glazing that are used in architectural applications include clear and tinted float glass, tempered glass, and laminated glass as well as a variety of coated glasses, all of which can be glazed singly or as double, or even triple, glazing units. Ordinary clear glass has a slight green tinge but special clear glasses are offered by several manufacturers. Glazing can be mounted on the surface of a window sash or door stile, usually made of wood, aluminium or PVC. The glass is fixed into a rabbet (rebate) in the frame in a number of ways including triangular glazing points, putty, etc.. Toughened and laminated glass can be glazed by bolting panes directly to a metal framework by bolts passing through drilled holes. Glazing is commonly used in low temperature solar thermal collectors because it helps retain the collected heat.