Cased is the name given to glass where the body of the article is made up of layers of different coloured glass; the layers can be transparent or opaque.
Other decorative effects can be achieved by including coloured threads in the outer layer as in Osiris, trapping air in a pattern between layers known as Air Trap or including different coloured crushed glass in the inner layer as with Moss Agate.
The outer layer can also be a shaded colour which is more intense at the top and dies away to the base or vice versa; this technique was given the name Nuancé by Stevens & Williams. To create a shaded outer casing, this entailed taking a gather of coloured glass and “blowing through the bubble”, which meant that the glass near the iron would be thick and the true colour but this would get weaker as the glass thinned out prior to the bubble bursting. A gather with the inner colour would be blown into the open ended bubble on the other iron, which would be broken off, and the article finished in the usual manner.
For an explanation and comparison of shaded and heat sensitive glass click here.