How to Glaze With Cobalt

Mix cobalt glaze in a well ventilated area.

Cobalt oxide and cobalt carbonate are used to create the intense blue color glaze used on stoneware and porcelain pottery. Cobalt carbonate is finer grained that cobalt oxide which makes it the preferred agent when mixing glazes. Cobalt mixed with magnesia forms a pink to blue violet color while a magnesia an iron mixture with cobalt will produce an intense black coloring. Mottled and streaked effects combine cobalt and rutile. Firing a cobalt and magnesia glaze at cone nine creates a blue color with red, pink and purple area.

Things You'll Need

• Mixing container
• Gram scale
• Dust mask
• Safety glasses
• Metal spoon
• Gertsley Borate
• Synthetic Bone Ash
• copper Carbonate
• Cobalt Carbonate
• Tin Oxide
• Bisqueware
• Soft bristled brush
• Kiln

Instructions

1. Measure and pour 12.8 oz. of Gertsley borate in a mixing bowl.

2. Measure and add 3.2 oz. of synthetic bone ash.

3. Measure and add 0.8 oz. of copper carbonate.

4. Measure and add 0.4 oz. of cobalt carbonate.

5. Measure and add 0.208 oz. of tin oxide.

6. Stir the ingredients gently and mix thoroughly.

7. Add water until the consistency of pudding that is not quite set.

8. Apply the cobalt glaze to bisque-ware with a soft brush.

9. Allow to dry for three minutes. Apply a second coat of cobalt glaze.

10. Fire at cone nine or 10. Allow the kiln to run the entire cycle and cool completely before removing the finished item.

Tips & Warnings

• Always mix glaze in a well ventilated area wearing a dust mask.

References

• Barisof Design: The Colbalt Glaze Gallery
• Frog Pond Pottery: Making Stable Glazes for Function Stoneware and Porcelain
• Central Clay: Glaze Recipies