In 2025, we celebrated the completion of our 20cf soda kiln, Moxie, and shed which sits in the back of the Watertown studio. Although we're always experimenting, this kiln mostly runs cone 6/7 soda firings. Our regular clays and glazes can all be used in the soda kiln and we have a growing lineup of soda specific glazes and slips as well.
Indigo Fire class students and independent study members will have access to soda firings throughout the year (except during winter hibernation), but we offer firings periodically that are open to the general public.
What is Soda Firing?
It's a firing technique that introduces soda ash (sodium carbonate) into a gas or wood fired kiln at some stage late in the firing. The 'soda' zips through the kiln and reacts with the silica inside to form a shiny layer of glaze on the pots within. Soda is most often done at the cone 10, but the process works at mid and low fire temps.
So what's the big deal?
Well, when the soda ash is sprayed into the kiln it completely changes the surface colors and textures. The soda melts glazes and often produces variegated, crystaline effects. Raw clay that would otherwise be matte will gloss up. And most importantly, flashing slips transform into pearly smooth surfaces.
You'll find lots of yellow, orange, and dark brown coloration on soda pots.
*pot by Maddie Gage
Because of the atmospheric reduction and soda effects, you can produce exciting surfaces with less fuss in the glazing process. Or, even more fuss! You decide :)
How to Find Success in the Soda Kiln
Flashing Slips & How to Use Them
Flashing slips generally have a lot of kaolin, a bit of sodium feldspar, and very little silica. Certain concentrations of kaolin become very color reactive in soda and wood atmospheres.
This mug by Ned features flashing slip and iron wash
These slips are best applied to leather-hard greenware, either by dipping or brushing. There is a perfect timeframe to add slip to your piece- Apply it to too-dry work and it may crack off! Apply it to too-wet work, and you might end up with a floppy pot.
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Flashing slips can be successfully used on bisqueware, but a thin application is essential. Talk to a staff member to get the lowdown on that.
Glazing Advice
We fire Moxie in reduction which prioritizes the flashing slips. With this in mind, we suggest taking advantage of the flashing slips and leaving parts of your work bare to let the soda work it's magic.
Glazing a pot entirely that's heading for the soda kiln is fine, but doesn't fully take advantage of the soda process.
This pitcher by Sarah Carroll shows the contrast you can get when pairing a dark clay body with pale glaze.
Look for glazes that are reactive to the soda environment and produce effects that you can't achieve in an electric kiln.
Wadding
When we spray soda into the kiln, all of the surfaces within the kiln can be fused to the shelf they are touching. That is why we use wadding to prop our work up off the shelf. Our wadding is a 50/50 blend of kaolin and Alumina.
When you bring your work to the studio, you should roll small balls of wadding and use the provided wood glue to adhere them to the bottom of your piece. Please use at least 3 wads per pot, and go easy on the wood glue! A small dot will do.
A properly wadded pot:
- has at least three, marble sized wads.
- is leveled and glued on well (but does not have wood glue dripping off it)
- has at least 1/4" of clearance from the pot to the shelf.
Pro tips:
- Wadding is also an aesthetic choice. Go for neat and equally spaced wads.
- Larger pots usually warrant larger wads.
- Broad pieces like trays require many wads. Remember that the clay gets soft in the firing and may sag or warp if not properly supported!
Soda Firing Registration
Indigo Fire semester students and members have the opportunity to purchase 1/2 cubic foot allotments of space in our soda kiln. We have space for about 25 participants in each firing.
Current students:
A discount code for upcoming soda firings is in your email inbox (just find the most recent monthly haps!)
There are also QR codes at the soda station in each studio.
Public Soda Firings 🔥
We host cone 6 soda firings that are open to the public throughout the year. Public firings are announced on our newsletter. If there's an upcoming public soda firing and space left, you can sign up here:
What to know:
- Registration comes with .5 cf of space and costs $45. You may purchase up to two allotments (1 cf) per firing.
- Registration does not include clay or bisque firings. Clay and glazes should be cone 6. No low fire clay plz.
- Participants may use slips and glazes at our Watertown studio.
- Registrations are not refundable. If you can't get pots ready in time for drop off, find a clay friend who can :)
- Completed soda pots will be stored for two months and then cleared out if not picked up.
- Soda firings are more chaotic than electric firings. Some pots will have kiln wash bits, soda drips, stress cracks or other firing defects. These do not warrant a refund and are part of the risk associated with a soda firing. We do everything in our power to keep your pots safe and produce the best results we can!
Preparing for Your Firing!
Measuring Your Work
Kiln space is sold in half cubic foot allotments. There are a few ways to see if you've filled your full allotment. If you're a math person, measure the length x width x height of your work then add all the pieces together. (Make sure to leave a bit of space for loading!)
If you're a visual person, we have a Laguna box and some cardboard rectangles to help measure. When placing works in the box, make sure to leave about .25" between each piece to account for loading buffer space.
Here are a couple examples of utilizing the box for visual measurements.
Where to Drop off Work
If you have registered for a firing, you should drop your work off at the studio a minimum of 1 week ahead of the projected firing date. Firing dates are subject to change, but the drop-off date will remain true unless we contact participants otherwise.
Wadded work should be placed on the wooden cart in the Watertown bisque area. A clipboard with a roster of participants will be on the cart- please check your name off when you drop off your work.
Any work that is dropped off late or does not make it into the scheduled firing will be prioritized in the following firing.
The instructional video below gives you the low-down on where things are at the Watertown studio!