I had the opportunity to use a wood fired kiln and explore a salt glazing technique at @aucklandstudiopotters
What an experience! We spent the term creating pieces ready for the two day firing. I had no expectations (or idea) what was going to happen or how it was all going to work. I rocked up early one Saturday morning bright eyed and bushy tailed ready to help stoke the fire 🔥 hoping my pieces were going to make it through!
When firing a salt kiln, salt is put directly into the kiln through special ports over the flame. This is done close to the end of the firing process when the clay is becoming slightly molten.
Inside the kiln, the salt releases sodium, which forms a new chemical bond with the silica that is in every clay-body. Together they form an atmospheric glass, a glaze carried by the flame that kisses the contents of the kiln with an uneven, directional and orange-peel-like surface. The clay can blush or flash orange from the atmospheric firing. The amount of salt glaze distribution on the pieces depends on where the pot is situated, how the kiln is stacked, how much salt is introduced into the kiln, and more. Each kiln opening is full of surprises!
The following images document the process from conception through to final product.
Raw clay being shaped into a vase:
Added glaze after a bisque firing:
After adding a glaze using the spray gun:
Special 'wadding' is made for the bottom of the pots so they don't stick to the kiln shelves. The recipe is basically a thick kiln wash, and consists of 50% kaolin and 50% alumina hydrate. We then rolled this mixture into balls and stuck them to the base with PVA glue.
Day 1 - Glazed pots ready for the wood firing:
The kiln is stacked and ready to be closed up:
Day 2:
7am - The fire is lit
8.15am - We were at 180 degrees
Then we sealed up the kiln using a mixture of newspaper and slip (watery clay). Love me a bit of Papier-mâché
11am - We were at 468 degrees. We rotated teams throughout the day who monitored the fire, kept it stoked and provided pots of tea and biscuits!
5.49pm - We were hitting 1153 degrees. It was getting hot!!! We added a vase of flowers on top for the kiln gods.
The team below are removing a spy brick to see wether the Cones have gone down. Cones are pieces of ceramic that help you gauge whether a kiln has reached sufficient temperature and whether the pottery will have been fired the correct amount. Cones measure 'heat-work', which is a combination of the temperature reached, and the time it took to become that hot.
Once the firing was over this is what the cones looked like:
6.40pm - Time for the sachets of salt to be tipped into the kiln. Earlier in the day a team prepared the salt. This was newspaper filled with pool salts and then wrapped into a sachet that could fit through small openings in the side of the kiln.
When the salt hits the fire a plume of white smoke arises from the chimney
Once all the salt was dispersed into the kiln we maintained the temperature so that the heat would carry it throughout the pots.
8.42pm - We closed up the kiln and let it burn itself out. Our job was done for today.
A few days later - We were back at the studio eager to open the kiln and see what the final products looked like.
And that's a wrap!