How much energy does it take to fire a pot?
There are many different factors that affect how much energy it takes to fire a pot. In this blog post, we explore three different factors that can affect the energy required to fire pottery.
1.) The energy efficiency of the pottery kiln
Kilns vary enormously in terms of their energy usage and efficiency. Some kilns may be cheaper to buy but use more energy when heating. Some older kilns are less energy-efficient than new ones with better heating elements and insulation. A very energy-efficient kiln will often take days to cool down to room temperature. The kiln used to fire pottery at Oxford Clay for example takes 13 hours to heat up and 33 hours to cool down!
2.) How many pots are being fired at once
The more pots that can be fitted into each firing the less energy it takes to fire each pot. In a bisque firing, pots can be stacked inside and on top of one another, maximizing the numbers fired. However, in a glaze firing each pot needs to be adequately spaced apart so no two pots are touching. Glaze becomes molten at high temperatures so pots that are touching, fuse together. Pots need to be organised in the kiln to take advantage of gaps, whilst still leaving a small space between each one - a bit like a 3D puzzle.
3.) The ‘firing schedule’
The duration and temperature pots are fired to is called a ‘firing schedule’. Each type of clay and glaze has its own ideal firing schedule. Some pots (such as large ones) need to be heated slowly over a long time to ensure they do not explode or crack in the kiln. Some glazes need to be heated to a certain temperature and held there for a specific amount of time. This is known as a ‘soak’ and it is used to ensure that substances in the glaze melt properly and evenly. At Oxford Clay, the pots are thin enough to be heated quickly (80oc-120oc per hour) during the glaze firing and need a 15-minute soak at 1260oc.
So how much energy does it take to fire a pot?
The energy-efficient electric kiln used at Oxford Clay requires approximately 19 kW.h for a bisque firing and 40 kW.h for a glaze firing. Here is the total kW.h needed to fire:
Marston Dish - 1.54 kW.h (total bisque + glaze firing)
Iffley Dish - 1.54 kW.h (total bisque + glaze firing)
The average washing machine uses 1 kW.h for an hour’s cycle, so the energy used to make a pot at Oxford Clay takes around the same as one and a half hours of washing machine use.
As you can see the energy used to fire a pot, using an effectively packed, energy-efficient kiln, isn’t as much as you might expect.