Flow blue was a type of transfer pottery produced by Staffordshire, England, potters beginning in about 1820. Sold mostly in the U.S. market, flow blue was similar to traditional blue-and-white pottery, except that the blue color was deliberately blurred, an effect achieved by adding a cup of lime or ammonia to the kiln during glazing.

English manufacturers of antique flow blue included Wedgwood, Johnson Brothers, Minton, Royal Doulton, and Swansea. Patterns ranged from Blue Danube to Idris to the classic Willow. As for the objects themselves, they included toilet wares and teapots, plates and platters, vases and garden seats, and even dog bowls.

One interesting subset of flow blue is the blue-marble effect. All-over patterns such as Lazuli lent itself to this look: When given the flow-blue treatment, the pattern would bl...ur so that from afar the object resembled a piece of carved, blue-veined marble.