Sienna

About Sienna

Sienna is a color achieved on traditional pottery by some Northern Tewa potters through manipulations of their firing process. For centuries, the Northern Tewa have made their pots using a base clay to make the form and then put an iron-bearing slip on the surface. When they polish that slip, it gives them a good background for their designs and fires to produce deeper colors. In a normal oxidizing fire, that iron-bearing slip with turn red as the pot heats up and it will retain that red after the pot cools. To turn the same pot black in the firing, they pour powdered manure on the fire and create an oxygen-reduction atmosphere.

At any point after pouring on the powdered manure, a piece can be removed from the fire and that oxygen-reduction process will be halted partway through, leaving the piece colored somewhere between a deep red and a deep black: sienna.

Some potters fire their pieces to be black, do whatever design work they have in mind and then come back with a blowtorch to "enhance" them. At a high enough temperature, the clay will re-oxygenate and start to turn sienna. It won't turn as red again as it would have been without going through the oxygen reduction process. To get a glossy black pot and retain some of the glossy redness, potters will use things like aluminum foil to cover sections of their pieces and then fire them to be black. Places that are unexposed to the high-carbon atmosphere stay red.

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