Thursday 3 October 2013

How to Make a Wood Ash Glaze

Glaze Mixing
Over the summer I've been doing lots of glaze testing, and one of these has been to find my own Wood Ash Glaze recipe. It's not an easy process. I gathered together several recipes found in pottery books. All of them had a different take on the process - and sometimes conflicting ideas! I tried out four of the recipes with varying success, but now I think have my own version.

Wood Ash

The first thing I had to do was get a source of wood ash. You need at least a kilo of good grey/white ash with as little rubbish in it as possible: the sort you get after a long hot fire. Luckily my sister happened to have some. This came from a mixture of wood species (Cherry, Eucalyptus and general woody plants from the garden) that had been pruned and burned over the previous summer in a chiminea. This meant the ash was very clean and without contaminants like soil, which you might get from a ground fire. Anyway, my sister had collected all this ash in a bucket with the intent on using it to mulch the raspberries; but instead I jumped in and she very kindly let me have it!

First of all I had to clean the ash. This I did by sieving it to get rid of any last bits of twig, stone, carbonised lumps, leaves etc. I sieved it twice using the same sort of sieve as a normal kitchen/household size rather than a glazing sieve: and I wore gloves, goggles and a mask by the way as this stuff isn't too good for you if inhaled. The photo above shows the powder that was left. As you can see it looks very clean. I decided it looked good enough to use just as it was. Many books talk about washing the ash by soaking it, rinsing it and then drying it back to a powder. But this sounded obsessive and unnecessary to me! Instead I decided to use this powder as the dry ingredient in a recipe like any other.

Sieving The Glaze

After lots of little test batches, I decided on my final recipe. This is based on one found in Stephen Murfitt's The Glaze Book. The main ingredients are:

Wood Ash 38
Feldspar 30
China Clay 20
Flint 12

Although I've also added a percentage of Red Iron Oxide. 

After measuring out the ingredients precisely using an electronic scale, I put everything straight into a bucket of water. Then stir! Simple really. Although it would be if I wasn't wearing goggles, a mask and gloves (the donning of which always seems to bring on fits of sneezing...) The pictures above show just a few stages of making up the glaze mixture, which include sieving it at least three times using a 60 mesh glazing sieve. The result is the lovely rose-pink colour of the raw glaze mixture in the last photo.

Dipping Pots

And then it's just a matter of glazing some pots. Above are a couple of photos showing me dipping a jug into the freshly made Wood Ash Glaze. And below are some photos of the latest batch of pots in their raw glazed state, ready to be packed into the kiln...

Jug with Wood Ash Glaze
Glazed Pots Waiting for the Kiln

At the moment I have no idea if these pots have worked. As I type, I'm actually waiting for the kiln to cool down enough so I can open it and see the final results. It's a bit of a nervous waiting game: it could go either way. Below is a test tile of what the glaze looked like during the testing stages. As you can see, it's a very nice simple wood ash glaze fired in an electric kiln. But tests are only tests, and glazes can behave completely differently when put on a pot. So we'll just have to wait and see...

Wood Ash Glaze Test Tile