|Iron Sulfate (in grams)
|Water (in milliliters)
This produces an iron sulfate solution that is a 50% concentration.
While wearing gloves and a properly fitted respirator, slowly mix the 50 grams of iron sulfate into the 100 mL of water and stir well with a wooden stick. Between uses, the iron will settle to the bottom of the container, but you can just stir it again to redistribute it back into the solution. The only consideration is that if the iron sulfate is not fully stirred back into the solution, the results will be very mild or pale (a light sepia shade).
The iron sulfate solution is brown in color and it is easy to see it during application. It works best if applied to bisque ware and then refired to cone 06 to fix the color on the surface, as it will dissipate if it is applied right before glazing the piece. After refiring, the color will remain in place at high temperatures (cone 6 to cone 13).
I wear gloves while working with soluble salts, and apply the iron sulfate solution with a bamboo brush directly onto the piece. I only apply one layer as this solution saturates fast and results in a very dark coloration of the clay. The results are somewhat unpredictable, but they are always interesting.
I only use iron sulfate on surfaces that will not be glazed, as clear glaze turns the sharp sepia tone into a dull brown.This recipe was shared by Sandra Torres in the December 2020 issue of Ceramics Monthly.