Flow Blue, or Flown Blue, was a type of transferware pottery which was similar to traditional blue-and-white, except that the blue color was deliberately blurred during the firing process.
Prior to the invention of Flow Blue, the aim of underglaze printers was generally to make the pictures on their pottery sharp and clear. However, suddenly, the whole aim became to blur the outline of the engraving. Colours that had moved, or 'flowed' in the glost oven started a fashion in printed wares that continued until the end of the 19th century.
It may be that this form of decoration originally occurred by accident - the result of materials left by chance in the container in which the pottery was fired. However, once established, the process became far from accidental, as may be seen in James and William Furnivals' recipes below. The result of the addition of such ingredients was that the colour of the printing spread, or flowed, into the glaze, creating a blurred appearance.
James Furnival's Recipes Flow for China Glaze 1 lb Nitre 1 lb Rock Salt 6 oz Potash Pounded fine, dissolved in hot water, sieved, and mixed with 60 qt china glaze.
William Furnival's Recipes Mulberry Flow (John Heath, Burslem) 10 lbs Whiting 50 lbs Red Lead 5 qts Muriatic Acid 10 qts Water The Lead to be added to the liquid slowly and gradually dried, then add the Whiting and mix all well together.
Dry Flow 50 lbs Lime 16 1/2 lbs Lead 5 lbs Salt 2 1/2 lbs Nitre Thoroughly mixed together.
(Transcribed from Furnivals' Recipe Book, Stoke on Trent City Archives ref: SD 1469/2)
Deep blue was the most popular colour, although other colours were given the same treatment. These included flowing mulberry, black, yellow, brown and green.
The first flown ware was produced prior to the reign of Queen Victoria, although it became most fashionable during Victorian times, with its peak - particularly in Canada and the U.S. - being during the 1840's and 1850's, with ironstone, or 'stone ware', being the favourite medium for its display.
The effect may be found on items of both table and toilet ware.