The Graal glass technique was invented by the designer Simon Gate in collaboration with the craftsman Knut Bergqvist at Orrefors Glasbruk, Sweden, in 1916. Today it is used in other countries but it is a Swedish speciality. It is used to obtain a decorative motif engraved on the inside of the glass wall.
Coloured glass is internally cased by a layer of crystal by blowing crystal inside it. Engraving with a roller , acid or sand, takes away the external coloured layer as the design sees fit, thereby producing crystal decoration of coloured background. The heated object, which is reheated, is covered with another layer of glass placed delicately from the outside surface and blown again so as to expand the decorative motifs.
A variation of the Graal technique is the Fishgraal one, also invented by Hald in the 1930s. He created the decoration by taking away, through engraving, a large part of the external surface thereby obtaining coloured decorations on an uncoloured background. The name is derived from the fact that the decorative motif of the first collection were fish.
Another variety was introduced in the 1930s: the Ariel technique. Crystal or thick blown coloured glass is engraved deeply following a drawing by sand-blasting. Once reheated, the object is covered with a thin layer of glass so that glass is captured within the grooves. An evanescent and ecocative decoration is produced.
In Orrefors recently, the Swede Per B Sundberg invented the Litograal technique, in which decorations and words on the inside wall are engraved by sand-blasting on a layer of ceramic enamel, producing a lithograph effect.