These porcelain vases were fired in a soda kiln. For those of you that don't know, soda firing is an atmospheric firing technique where “soda” is introduced into the kiln near 2350°. The soda that we use is sodium bi-carbonate, also known as baking soda and sodium carbonate. The soda vaporizes when it is sprayed into the kiln and is carried on the flame throughout the kiln. The soda vapors create a glaze when it lands on a piece. This means you can leave pieces unglazed on the outside and allow the soda and flames to work their magic on the surface.