How to make bone ash for pottery glazes

A very lovely fellow potter gave me a recipe for a white glaze called ‘Neil Hayes 1’, as pictured below.

NH1 on A speckled clay body

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.

Some recipes including bone ash as an ingredient

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.

Let’s not support factory farming

While I do eat meat, I am very careful to only eat meat that I believe has been sustainably & ethical farmed. 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.

I started looking into how hard it would be to make myself, and decided I would give it ago. 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.

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.

Me on my in-laws farm in the Coromandel. They also raise sheep and cattle.

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!

My process

So the steps that I took in order were:

  1. I went to my local butcher shop and bought 5 kg of cattle bones for $7
  2. I boiled the bones for about 5 hours in 10L of water to make bone broth
  3. Drain and dry the bones, removing as much meat, cartilage etc
  4. Put the bones in a greenware bowl with a plate on top or a lidded jar and bisque fire
  5. Grind up the bones with a mortar and pestle – or I used my BlendTec blender (Witchy but make it modern)
  6. Make sure you sieve your glaze after it is made up 🙂

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 🙂

Author: niceassets

Kia ora, I'm Nicole of Nice Assets Workshop. I put the ‘fun’ in functional ceramics with sustainable and socially conscious ideology underpinning my pottery.

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