In my previous posting I mentioned "Flow Powder" put in the saggar to promote the flowing of the printed color. I thought that it was also used in the glaze and have now found a contemporary description to support that.
In 1846, William Evans published his small booklet "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' to give them the "same powers of ratiocination as the most wealthy of their employers". Looking up the word ratiocination I understood this to mean that in disputes, the workers would have the same information as their employers and thereby form more effective arguments in bargaining with the manufacturers. Of course if all else failed the Potters Emigration Society could carry the disaffected to a new life in the USA.
On page xi of the Preface 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,[recipes] 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."
Appendix p. 64
"FLOWS FOR BLUE
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."
I am no ceramic chemist but I think the recipes would flux (lower the melting point)the glaze,and produce a chemical that encouraged the printed color to flow.
Evans description shows that there is rarely one single way to do something in the ceramic industry, he writes that flow blue has "undergone several changes" and then describes the latest change and gives three alternate recipes - no doubt there were others.
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