Flow Blue

flowFlow Blue
At some time in the late 1830s-1840s a new species of blue printed pottery was introduced into the marketplace and was particularly popular in the Unites States. Known as flow blue, its main characteristic was that the blue printed design was encouraged to flow or seep into the glaze during the firing process. The amount of flow or seepage varies from a light blurring of the pattern to a flood of blue that almost obscures the design.

How flow blue came to be developed as a legitimate pottery decorating technique is yet to be discovered.  How it was produced has been documented showing that there were at least two ways to encourage the cobalt blue printed design to flow into the glaze.  The potter could use either a flow glaze or place a flow powder in the saggar* during firing.

Flow glaze
In 1846, William Evans published the Art and History of the Potting Business. Evans was a trained Staffordshire potter, publisher of The Potter's Examiner and Workman's Advocate newspaper and instigator of the Potters Emigration Society. The preface of the book asserted that the book was intended to take the secrets of pottery manufacture out of the hands of the employers and to make them available to working potters so they would be able to form more effective arguments in bargaining for increased wages and better working conditions. Of course if all else failed the Evans’ Potters Emigration Society could carry the disaffected to a new life in the USA.  Evans writes: 

"I am fully aware, that the question with potting manufacturers, is not so much the advancement of the art, as the discovery of cheaper processes and cheaper materials, by which the present quality of manufacture can be wrought. To this end the enquiry of nearly all practical potters is now directed. The flow, for blue, although of recent introduction, has undergone several changes. That, now in use by W. Ridgway, Esq., is considered to be the best. Instead of washing or placing the flow in the saggars, it is introduced in the glaze; and a great saving of expense is thereby secured. 

   The Flows, inserted in the appendix to this work, have been sold, and re-sold at an exhorbitant price, when first introduced in potting manufacture. Those recipes were sold, on two successive occasions for £100 each time, and are now prized by Messrs. Boyle, Dimmock, and Meigh, as the best in use."

Evans includes the following flow recipes in his Appendix 

 No. 1. __ 12 of Linn, 1 of sal ammoniac, 2 of red lead. 
No. 2. __ 4 of Linn, 1 of common salt, 1 of soda 
No. 3. __ 21 of whiting, 4 of lead, 4 of salt, 2½ of nitre." 

Flow wash and Flow powder
When Evans speaks of using the flow in saggars he is referring to the use of a flow powder that could be placed into each saggar or could be mixed to a liquid and washed over the inside of each saggar. During firing the chlorine in the flow material would vaporize and combine with the cobalt blue in the print rendering it slightly soluble in the glaze.  

 *saggar – a protective earthenware box in which pottery is placed and is then stacked in the oven during firing.

Evans, William 1970, ‘Art & History of the Potting Business (1846)’ Journal of Ceramic History No. 3. Stafford: City Museum & Art Gallery, Stoke-on-Trent.

Dodd, Arthur Edward. 1964. Dictionary of ceramics: pottery, glass, vitreous enamels, refractories, clay building materials, cement and concrete, electroceramics, special ceramics. London: Newnes.