In Silversmiths in Elizabethan and Stuart London, (London 2017 p.154) David M. Mitchell attributes this maker’s mark to Thomas Cooper, son of William Cooper of London, goldsmith, who was apprenticed to the plateworker Thomas Aylinge for eight years from Michaelmas 1660. He became free by service on November 4, 1668. Between 1669 and 1691 he had six apprentices, the last being Gabriel Sleath who became free by service in 1701.  Cooper died about 1691.  Mitchell identifies the fish in the mark as a dolphin and lists examples of plates bearing this mark between 1667/68 and 1692/93 including porringers, chalices, tumblers, beakers, plates and communion cups.

The chasing on this tankard is done with unusual depth and some freedom. The chaser has not followed exactly his preparatory dotted outlines. The scene mixes exotic plants and fanciful birds with classical motifs. The front shows a baroque fountain with dolphin supports, female figure stem and dragon spout. The body of the fountain recalls Bernini’s Fontana del Tritone in Rome. The figures flanking the fountain likewise are classically derived.

A fountain in the form of a triton riding a dolphin appears on a chinoiserie  mirror, maker’s mark only D in script, circa 1685, formerly in the Jaime Ortiz-Patiño Collection, sold Sotheby’s New York, May 21 1992 Lot 154 ($77,000). A baroque fountain appears on the cup and cover probably by John Ruslen, 1680, in the Collection of the Worshipful Company of Goldsmiths illus. David M. Mitchell op. cit p. 392.