Kilns, Planes and Automobiles: CO2 Emissions From My Ceramic Firings

Like most potters, I am sure, I have had concerns about the emissions produced from firing clay work to over 1200° Celcius (>2192° F). I do sometimes wonder, is it even right to carry on when the world is overheating?

I use both an electric kiln of 300 litres and a fibre-and-brick-lined gas kiln I made myself of slightly less practical volume.

I have been making the assumption that the electric kiln would be less carbon producing, based on the fact that the power is produced by efficient industrial processes — versus my own clumsy attempts to fire in gas reduction. But I didn’t know that for a fact.

Today I had the urge to actually try and find some numbers to see what is the difference in emissions between the two types, and how does it compare to large consumer-based emission sources like aeroplane flights and car use. I chose transport as a frame of reference because it is something that most people engage in frequently is considered a ‘normal’ activity in society — rather than some other industry.

I did find some numbers online that give me a general idea of my emissions. Of course, they are based on statistical data and the electricity produced in Croatia may well be less or more efficient than in another country. But the comparisons are quite sound as a general guide, I think.

Gas firing

So, for a glaze firing in the gas kiln to around cone 8/1247°C/2277°F (an average of the top and bottom temps), I tend to use around 20 kg of butane (I know, it’s better to use propane but it’s hard to access where I live, and I manage despite freezing bottles sometimes). This number is not exact, but I know I roughly use two 10 kg bottles each firing.

According to calculations from this study article, complete burning of butane produces CO2 in a roughly 1:3 ratio (3.03 actually). So, theoretically my firing produces, around 60 kg (132.2 lb) in CO2 emissions (20 x 3).

Since I fire in a carbon-heavy reduction atmosphere from around 900°C/1652°F and up, which is incomplete burning, this CO2 number is slightly less, and some small amount of unburned butane will be emitted too. Plus a lot of water vapour which is produced as the butane molecules are split.

Electric firing

Over to the electric kiln: Carbonfund.org states that CO2 emissions from the production of 1 kWh of electricity come to around 0.3712 kg (0.857 lb) of CO2. This is for average US production but I imagine it is not too dissimilar over here in Croatia.

In a recent cone 7/1237°C/2259°F glaze firing of my electric kiln (packed with pots), I used 71.5 kWh of power (I do note down the meter readings). This equates to 26.54 kg (58.51 lb) of CO2 (71.5 x 0.3712).

So, yes, that is far less than the gas kiln, though I fire 1-2 cones cooler in the electric, and produces roughly a third of the emissions.

Flight emissions

But these numbers are small compared with plane flights, even on an individual share basis.

Carbon Independent says the following:

“CO2 emissions from aviation fuel are 3.15 grams per gram of fuel, which gives CO2 emissions from a Boeing 737-400 of 115 g per passenger per km. At a cruising speed of 780 km per hour [Wikipedia, 28.2. 08], this is equivalent to 90 kg [198.41 lb] CO2 per passenger per hour.”

So even my gas firing of 20-30 pots is only two thirds of 1 hour of cruising flight for one passenger. The electric is much less.

And if I, say, took a solo holiday trip of 4 hours each way, the CO2 for my share of the flight would be around 720 kg. In effect, I can fire the gas kiln 12 times and produce around the same CO2 as a trip on my own to, say, Istanbul, from Zagreb. The electric could be fired roughly 27 times to match the same flight! (More, actually, as I now fire to cone 6/1220°C/2228°F.)

It is worth noting that other organisations cited on the Carbon Independent page estimate the per hour/per passenger emissions much higher: from 134 – 350 kg CO2.

I only fire the gas kiln every 2-3 months, as I’m using the electric more these days.

And what about cars?

For another common frame of reference, we can look at cars. The US EPA says:

“A typical passenger vehicle emits about 4.6 metric tons of CO2 per year. This assumes the average gasoline vehicle on the road today has a fuel economy of about 22.2 miles per gallon and drives around 11,500 miles per year. Every gallon of gasoline burned creates about 8,887 grams of CO2”.

So, over a year, if I fire the gas kiln 7 times and the electric 12 times for glaze firings, I would produce 678 kg of CO2 approx. — way less than running an average US car: 4.6 metric tons equates to 4,600 kg of CO2.

In actual fact, it is more complex. My pots (as with most ceramics) are fired two times, with a low-fired 1,000°C/1832°F ‘bisque’ firing before glazing, then a glaze firing to top temp.

This bisque firing will produce around half the CO2 of a glaze firing to full temperature. So based on the 17 glaze firings, I should estimate my annual emissions at 678 kg (glaze) + 339 kg (bisque) = 1,017 kg. Still way less than a quarter of the emissions from running an auto for a year and less than one person’s share of a return 6-hour flight (remember, for a year’s-worth of firings).

My thoughts and plans

While any effort to reduce emissions is obviously beneficial for the planet, I think in context my level is very low, especially as a small (artistic) production business. My feeling, and that of most potters I think, is that our small contribution to emissions is worth it to have the joy of art in the world, and to have artists be able to make a living doing what they love.

There are so many other major, major, emitters of CO2 should be brought into the modern world and drastically cleaned up, like freight container ships and coal power plants, before we potters should be under pressure to make drastic changes. That’s not to mention the thousands of empty flights we have seen since Covid times. Or billionaires flying solo in the executive jets!

But potters are not without responsibility to try and improve the situation either.

I do intend to continue to develop beautiful glazes for the electric at cone 6 to minimize how often I need to fire with gas. To get certain glaze effects and colours I have to fire in reduction sometimes. I am working on reduction glazes that I can fire to lower temperatures too.

I am currently researching the cost and how-to of getting some solar panels. It looks like it would be quite easy to produce all the power for the electric kiln and more with panels I could put on my roof. My house faces south on one side and I get strong sun from dawn till dusk, so I think it could be a good solution.

Australian potter Steve Harrison has set up a system for this and I imagine it must be a great feeling to know your kiln is not emitting CO2 at all.

If all this reads like I am trying to persuade myself that it is all ok, that’s definitely true. I have been worried about my CO2 contribution. So, it is something of a relief to do the research and find that I am having quite a minimal environmental influence. Thanks, mathematics!

And I hope in the near future I can make my emissions far less, with a little expense, which is an investment in the planet as I see it.

Is it appropriate to compare pottery firing with flights and car use? What do you think about the dilemma of emissions vs producing ceramic art? Did I use any faulty logic? Leave me a comment below.

Featured image: Photo by Ben Klewais on Unsplash