The part of the window in which the IGU is mounted. See casement window.

Casement fastener

Closing hook for casement and top hung windows. When the window is closed the fastener is secured in a tail hook fixed on the window frame or the mullion. Also called a pullback.

Casement stay

A catch to keep the window in an open position. It is fixed to the window sash or the frame and is secured in a tail hook when the window is open. Also called a catch.

Casement window

A window that opens on hinges like a door. With a closing mechanism (fastener).

A four-light casement window, the outline of which may be compared to the Danish flag “Dannebrog”: The two lower casements are about twice the height of the top sashes. Mullion and transom forms a cross, and the window is usually called a “cross window”. The window is common in residential houses from the 18th and 19th centuries. Also short form ‘casement’.

Cast iron window

Window of which frame, sash and muntins/mullions are made of cast iron. They may be hinged.

Cement Groove

Milled groves on the outside of the frame. When the window is installed the rebate is filled with sealant to draught proof between frame and wall. Also called joint rebate.

Child safety lock

A device to prevent easy opening the window further than ventilation position. May be individually installed or integral in handles or other fittings.

Classicist window

A window from the architectural style Classicism in the period 1780-1835. The typical window from that period is shaped like a casement window with muntins.

Coated glass

A film or coat applied to the glass surface featuring sun protection or energy saving. See also energy pane.


Homogeneous material made from two or more constituent materials with significantly different properties. E.g. plastic fibreglass. Most composite material can be used for spray moulded extruded or pultruded components.


Vaporized water on e.g. a pane. May occur outside or inside, when the glass unit is colder than the surroundings. By severe low temperatures ice flowers can form on the inside of the pane.

Cone finial

Cone-shaped ornamentation on top of a loose-joint butt.

Corner bracket

A metal plate mounted on the corners of the window casement/sash to strengthen it.

Corner hinge

An inset hinge as part of a corner bracket.


S-shaped moulding on e.g. mullions and muntins. 

Coupled casements

Two separate window sashes/casements jointly hinged to the frame. The sashes/casements are coupled together by coupling brackets or coupling bolts.

Cross window

Four-light casement window with a mullion and a transom forming a cross. The outline may be compared to the Danish flag “Dannebrog”, therefore called Dannebrog window with muntins.

Crown glass

Early type of window glass, also called moon glass. In the process, glass was blown into a "crown" or hollow globe. It was then flattened by reheating and spinning out the bowl-shaped piece of glass (bullion) into a flat disk by centrifugal force. The glass was then cut to the size required.

Known as bull’s eye (or Oeil de Boeuf), the centre area, which was thicker than the rest, was used for less expensive windows.


Double glazed insulating pane (DGU), where the edge sealant fits tightly to the edge of the glass sheets. The air spacer bar is made of lead and filled with a humidifier. The spacer is soldered on to both glass units using lead. The insulating pane was marketed under the name Cudo. Today referred to as an “old fashion DGU”.

Curtain Wall

A term used to describe a façade which does not carry any load from the building itself. The construction may have panels or sections of glass or isolated panels of other material, e.g. solar cells.

Cylinder glass

A type of glass made by a method developed about 1100. A glass blowing pipe with a lump of glass is swung over a large trench while rotating. The lump is blown into a cylindrical iron mould. The ends are cut off and a cut is made down the side of the cylinder. The cut cylinder is then placed in an oven where the cylinder unrolls into a flat glass sheet.