During steel casting, the steelmaking ladle is emptied through a valve in the bottom of the ladle; as the ladle gradually empties, the ladle top slag coats and solidifies on the side walls of the ladle, and remains there once the ladle is empty. This is termed 'slag glaze' as it glazes the surface of the ladle walls.

The next time the ladle is used, the steel tapped into the ladle interacts with the slag glaze in a similar way to the ladle top slag, influencing the steel inclusion population. Some of the glaze also re-melts and floats to the surface of the ladle and is incorporated in the ladle top slag.

Because of the interaction between steel and glaze and the resultant impact on the inclusion population, for some steels it is very important to ensure that the ladle glaze has the correct composition; this helps to ensure that inclusions of a desirable chemistry are formed.

To control the ladle glaze, it is necessary to carefully plan that the steel made in a ladle just before an inclusion critical steel grade, is of a certain composition and made using a specified ladle top slag (which forms the glaze on the inclusion critical cast).