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A very lovely fellow potter gave me a recipe for a white glaze called ‘Neil Hayes 1’, as pictured below.
It’s a lovely glaze but included an ingredient I hadn’t used before – bone ash.
You can find a huge variety of glaze recipes using bone ash on Glazy.
According to Wikipedia:
Bone ash is a white material produced by the calcination of bones. Typical bone ash consists of about 55.82% calcium oxide, 42.39% phosphorus pentoxide, and 1.79% water. The exact composition of these compounds varies depending upon the type of bones being used, but generally the formula for bone ash is: Ca5(OH)(PO4)3. Bone ash usually has a density around 3.10 g/mL and a melting point of 1670 °C (3038 °F). Most bones retain their cellular structure through calcination.
You can read more about bone ash as a glaze material on Glazy.
I don’t need to go into all the details of why factory farming is bad here, but if you want to learn more, check out the Humane League for info on why factory farming is bad for animals, people, and the environment.
You can also read about and support SAFE’s work in NZ.
I tried enquiring at my usual suppliers (CCG, Nelson Pottery Supplies) to find out where their bone ash was from. All they could tell me was that the bone ash was imported from the UK. Some suppliers also sell synthetic bone ash, which is also imported from overseas.
We have plenty of bones here in New Zealand so I started looking into how hard it would be to make myself.
I know cattle are raised as grass-fed and free range animals in New Zealand as I have seen on my in-laws farm, so I felt comfortable about buying bones from my local Halal butcher shop.
There was not a lot of information online, so I asked on my local pottery group’s Facebook page. I didn’t get responses from anyone who had done it, but I did get some general suggestions.
To calcine materials you usually need to fire to a bisque temperature. So I understood what I needed to do was easy enough – get some bones, put them through a bisque firing in my kiln, and grind them up.
Ultimately I decided to just experiment and see what would happen if I made my own bone ash, and made the glaze above with it, and I’m pretty happy with the results! Bonus you get homemade bone broth!
So the steps that I took in order were:
Some photos of the process:
So that is how I made my own bone ash! It’s really easy and it feels really great to be able to use locally sourced materials in my glazes 🙂
Thank you so much for sharing your process! I’m going to try it out myself with some bones from an organic farmer. I’ve been eyeing those pretty khaki glazes, but didn’t want to buy regular bone ash. But this gives new possibilities!
Ha, bones from cows. Not the farmer himself 😛
I’m hoping to do this with my pet cat who was killed yesterday (obviously will be skipping the broth part), we’re going to bury her for a few weeks first so the soft tissue decomposes, then leave the bones to dry in the sun.
What cone did you fire to in the end?