Iron Red Glaze
Iron red glazes are common in the cone 6 range. The red color is a product of iron silicate crystals forming during the cooling cycle in the kiln. These glazes depend on having a very fluid melt. While it seems logical that a slow enough cooling cycle during firing is important to give the red iron crystals time to grow, in actual practice we have not been able to confirm this. While a thick application is needed to encourage the crystallization, if applied too thickly iron reds will run down off the ware. Thus experience is needed to achieve a workable thickness to be able to manage vertical surfaces. Try to apply the glaze just thick enough that you can tolerate the amount of running.
Iron Red glazes look a little different in a flow tester
Melt flow test comparing two cone 6 iron red glazes fired to and cooled quickly from cone 6. Iron reds have very fluid melts and depend on this to develop the iron red crystals that impart the color. Needless to say, they also have high LOI that generates bubbles during melting, these disrupt the flow here.
G2896 Ravenscrag Plum Red iron red cone 6 glaze
Original development of this recipe was done to match the chemistry of Randy's Red (a popular recipe). At the time we did not do any special firing schedule to encourage the growth of the red crystals.
Ravenscrag iron plum red. Why different colors?
The one on the right was cooled slower. Controlled cooling in the kiln is a key to developing the color.
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