Dresser included Celtic inspired designs in most of his published works, and produced commercial graphic designs with Celtic themes from an early stage of his career. His Dragon design wallpaper of 1867 is a typically innovative synthesis from a dog grotesque in the Book of Kells, and a knotwork pattern published by Owen Jones in Grammar of Ornament.
Dresser knew both these sources well. In 1867 he mentions studying the grotesques from the Book of Kells in Westwood's The Art of Illuminated Manuscripts. This contains the illuminated capital letter "T" as a dog grotesque (shown above left rotated 90 degrees clockwise). Dresser also had intimate knowledge of Grammar of Ornament. It was written by his tutor and mentor, Owen Jones, and included Dresser's first published work - he did the artwork for one of the book's colour plates.
These sources provide several of the decorative details used on the Elkington Jug. Illustrated below left is a knotwork pattern repeated around the Jug. This, and the engraving on either side of the Jug's spout, (below right), are both derived from Grammar of Ornament. The handle of the Jug is decorated with an interlaced dragon pattern (not shown here) taken from the initial letter in Plate 1 of the Book of Kells as illustrated in The Art of Illuminated Manuscripts.