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Troubleshooting Commercial Underglazes

Troubleshooting Commercial Underglazes

Ceramic Glazes

Have you experienced issues with commercial underglazes? Participate in my underglaze research project and help me find solutions for underglaze firing defects.

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Inconsistent Glaze Results? Download this free guide

Download a pdf of my Understanding Cone 6 NCECA presentation

Recent Posts

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    Glazy Demo – Adding Recipes and More

  • Why Specific Gravity Isn’t Listed on Glaze Recipes

    Why Specific Gravity Isn’t Listed on Glaze Recipes

  • 5 Reasons Why Your Large Batch of Glaze Doesn’t Match Your Test Batch

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  • A Clay Reclaim Process Using a Pugmill/Clay Mixer

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  • How to Make a Cone Pack

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  • Commercial Glazes vs Mixing Your Own – A Cost Comparison

    Commercial Glazes vs Mixing Your Own – A Cost Comparison

  • 99 Cone 6 Glazes You Can Try

    99 Cone 6 Glazes You Can Try

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    What Glazes Can You Make with Limited Materials?

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    How to Measure Specific Gravity – Clay Week 2020

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    How to Fix a Hard-Panned Glaze with Epsom Salts

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suemcleodceramics

🤓 I teach online courses about glazes. Join my Facebook group - Understanding Glazes with Sue for glaze troubleshooting 🤓
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Sue McLeod
I encourage all potters to include at least one co I encourage all potters to include at least one cone pack in every single firing. Whether you're firing a manual kiln, or a digital kiln, witness cones provide important information about the firing that you otherwise won't have at your fingertips.⁠ ⁠ Making cone packs a habit in your firing will help you troubleshoot any clay and glaze issues that come up. You never know when you’ll need them until it’s too late.⁠ ⁠ If you’ve never used witness cones before, begin by putting one cone pack on every shelf of your next firing. This will give you really good info for how accurately and evenly your kiln is firing.⁠ ⁠ Remember, a full-colour downloadable PDF version of my blog post on cone packs is available on my website, which you can access via link in bio.
Step by step, this post walks through my process o Step by step, this post walks through my process of making cone packs. In these photos you'll see me making a cone 06 bisque firing cone pack, so I’m using cones 07, 06 and 05. The process is the same for a glaze firing cone pack. ⁠ ⁠ Make sure the clay you’re using for the cone pack is rated for your glaze firing temperature or higher, or the clay will melt. And, as I emphasized previously, make sure you are placing your cones in the correct order!⁠ ⁠ My whole article on this topic, including a printable PDF version, is available on my blog, via link in bio.⁠ ⁠ Have you made your own cone pack before? I'd love to hear about your method in the comments below!
Here is quick but important side note about making Here is quick but important side note about making cone packs for your bisque firing. Keep in mind that low temperature cones are usually all the same colour – red. This means you have to be very careful to put them in the correct order in the cone pack.⁠ ⁠ 🔥 Low temp cones are numbered with a 0 in front and the number after the 0 decreases as the temperature increases.⁠ ⁠ 🔥 For example, cone 08 is a lower temp than cone 07. As temp increases, the cone numbers go down – 06, 05, 04, 03, 02, 01 and then they start at 1 and go up – 2, 3, 4, 5, 6 etc.⁠ ⁠ 🔥 So cone 06 is a much lower temp than cone 6. Pay close attention so that you don't mix these up! It can and does happen!⁠ ⁠ 🔥 The next thing to remember when making your low temperature cone pack is that the higher numbered cone will melt first.⁠ ⁠ 🔥 So in a cone 06 firing, I would use cones 07, 06 and 05. Cone 07 melts first and needs to be at the “front” of the line. Then 06, then 05.⁠ ⁠ 🔥 In contrast, for a cone 6 firing, the cone 5 melts first, then cone 6, then cone 7.⁠ ⁠ If you put the cones in the wrong order so the low temp cones fall on top of the higher temp cones, you won’t get a good reading. I’ve done this before! Swipe through to see what it looks like after the firing. Not very accurate.⁠ ⁠ As ever, if you'd like a printed version of these guidelines to refer to as you make your cone packs, you can find the full colour PDF version via the link in my bio.
If you want to achieve more consistent results wit If you want to achieve more consistent results with your glazes, firing to firing, placing at least one cone pack in every firing is part of the work that will get you there.⁠ ⁠ A cone pack is a set of 3 large pyrometric cones that are set into a small piece of clay so they can stand up on their own, visible to you through one of your kiln’s peep holes during the firing.⁠ ⁠ If you’re new to using pyrometric cones, aka “witness” cones, they can be purchased as “self-supporting” or regular “large” witness cones.⁠ ⁠ Small “kiln sitter” cones or pyrometric bars should not be made into a cone pack and used as witness cones. They are meant to go on the kiln sitter cone supports in a manual kiln and they’re only accurate when used for their intended purpose.⁠ ⁠ The self-supporting cones are a little more expensive, but they can just be placed on the kiln shelf without any prep beforehand. They don’t need to be made into a cone pack because they stand up on their own.⁠ ⁠ Regular large witness cones are what I use in my method of making cone packs. ⁠ ⁠ Now that we know which cones we're using, there are important details about placement and angle within the cone pack. Swipe through to learn more. And if you want to read the full article on my blog, you can find it via the link in my bio.⁠ ⁠
Possibly my posts last week have swayed some potte Possibly my posts last week have swayed some potters to begin adding witness cones in every firing. If you're a new follower or just catching up, my hope last week was to help explain how important witness cones are for getting an accurate measurement of the heatwork that's affecting your clay and glazes. More than that, the information that witness cones contain can also help you know when your kiln might need some maintenance.⁠ ⁠ In my previous post, I briefly summarized the different types of witness cones that you can purchase. Self-supporting cones can be placed directly on your kiln shelf with no additional prep required. They're a little more convenient, but also a little more expensive.⁠ ⁠ Regular large cones need to be propped up at a specific angle in order for them to work properly. You can buy a cone holder to place them in, or you can make your own "cone packs" using a coil of clay. This is how I've always done it and I wrote a blog post to demonstrate how you can make your own cone packs. You can read it via link in bio.⁠ ⁠ In the next few posts, I'll be sharing my approach to making cone packs using regular large cones and a coil of clay. Loads of experience, including mistakes I’ve made with cones along the way, have helped me develop and hone this approach. I hope this will help you see how easy it is to include witness cones in every firing and to avoid the mistakes I have made so you get the most accurate reading of your firings from this point forward.⁠ ⁠ ⁠ #kiln #firing #cones #witnesscones #glaze #ceramics #pottery #conepack
I hope you've been enjoying my series on witness c I hope you've been enjoying my series on witness cones. More info coming next week. I sincerely hope that if you’re not using witness cones in every firing, you will begin to add this step in your firing practice. You just never know when you’re going to wish you had the information that they provide. ⁠ ⁠ Looking closely at the cones from every firing, even ones that go well, will help you begin to connect slight temperature changes with your glaze results.⁠ ⁠ The magic often lies in the details.⁠ ⁠ Some glazes can be finicky when it comes to temperature. I have a glaze that needs to be fired to where the tip of cone 6 is touching the kiln shelf and cone 7 is just starting to bend. Any cooler and the glaze is flat with no variation. Any hotter and it runs onto the kiln shelf.⁠ ⁠ It took me a while to figure out why my glazes were never turning out the same. I kept trying to change my application methods. Then I finally put a cone pack on every shelf and it all made sense. The bottom shelf was slightly cooler than the rest of the kiln and this particular glaze needed to be fired hotter. I wouldn’t have known this without cones.⁠ ⁠ This knowledge helped me plan my kiln loads for success! I now load my more versatile glazes into the bottom and my finicky glaze is loaded into the top. I also make sure I can see the cone pack through the peep on the shelf with that finicky glaze. I don’t let the kiln shut off until that cone pack looks exactly how I want it. ⁠ ⁠ Great glaze results = happy potter!⁠ ⁠ If you are a new follower, you might like to know that I provide a downloadable full colour pdf version of my blog post, which you can access via link in bio.⁠ ⁠ To review the information and reinforce your understanding of this topic, you might also want to watch and listen to my video, "Ceramic Story-time with Sue," where I read the blog post live inside my Facebook group and answered questions. The video is embedded right there towards the bottom of the article.⁠ ⁠ I try to make it accessible and welcoming for all. If you haven’t checked out the complete blog post yet, you can find it via the link in my bio, with the downloadable pdf and video versions!
When you use 3 witness cones, not only can you tel When you use 3 witness cones, not only can you tell if your kiln was under- or over-fired, but you have a detailed picture of how close you were to your target cone. This info is crucial for understanding your glaze results and making the proper adjustments to your firing schedule for the next time.⁠ ⁠ #kiln #firing #glaze #glazefire #glazeresults #heatwork #kilntemp #ceramics #pottery #witnesscones #conepack #ortoncones #pyrometriccones
With a deeper appreciation for the work that pyrom With a deeper appreciation for the work that pyrometric cones do in firing, and for the information they provide you when a firing is complete, let’s consider which cones to use when firing. I generally put three witness cones in my firings. This includes one cone for my target temperature, one cone just below the target and one cone above it. In a cone 6 glaze firing, I would normally use cone 5, cone 6 and cone 7. The images from this post document a firing when I had run out of 5s so I used a cone 4 instead. Any cone lower than your target cone will let you know you're approaching temperature so you can be ready. 🔥 Cone 5 is the Guide Cone. It starts melting first. When cone 5 starts to bend, you know the firing is approaching its peak temperature and you can get ready for the cone 6 to start bending. 🔥 Cone 6 is the Target Cone. This is the cone you want to be perfectly bent so the tip is pointing down. That’s when the firing is complete and you can shut the kiln off if it doesn’t shut off automatically. 🔥 Cone 7 is the Guard Cone. If you don’t happen to be watching your cones as they bend and your kiln over-fires, the guide cone will tell you if it is way over-fired or only slightly over-fired. In a cone 06 bisque firing, I’ll use cones 07, 06 and 05. Cone 07 is the guide cone because it melts first. Cone 06 is the target cone and cone 05 is the guard cone. It’s likely clear to you at this point why cones are essential when firing a manual sitter kiln. Without a thermocouple or pyrometer to tell you the temperature inside the kiln, witness cones are your tool for making sure your kiln fires to the right temperature in case your Kiln Sitter malfunctions (as I said before, it can happen!) Even if you have a digital pyrometer, I still recommend witness cones in every firing. They’ll give you more accurate information about your firing than a digital temperature reading. This is because of heatwork, the subject I pick up in my next post! If you want to keep reading, follow the link in bio to access my article on this topic. #kiln #firing #glaze #glazefire #glazeresults #heatwork #kilntemp #ceramics #pottery #witnesscones #conepack #ortoncones
Let’s look a little more closely at cones, to un Let’s look a little more closely at cones, to understand the different cone types and their purpose in firing your kiln. If you read my post last week about the kiln sitter, you already have a preview of how small cones work in the kiln sitter mechanism to help control when the kiln shuts off. In this post, I focus on what's happening to the pyrometric cone in this process. ⁠ ⁠ It's also important to understand the significant work that larger cones do in a firing. Swipe through the images above to really appreciate why they're called “witness cones." After a firing, we can turn to these large cones for important information about how the firing went. They're a visual representation of the heatwork within the kiln. ⁠ ⁠ Ideally, witness cones are located where you can see them in the kiln during the firing by looking through a peep hole. When you see the cones bending, you know the firing is reaching its peak temperature. ⁠ ⁠ With this visual guide, you can prevent your kiln from shutting off too early or too late. In the event that your Kiln SItter malfunctions (it can happen!), witness cones help you ensure that your kiln fires to the right temperature.⁠ ⁠ Follow the link in my bio to read my complete blog post on this topic, and swipe through the images here for more information to expand your understanding of the firing process and your control over your glaze results!⁠ ⁠ #kiln #kilnwork #pottery #ceramics #kilnfiring #heatwork #cones #witnesscones #pyrometriccones #clay
I receive a lot of glaze troubleshooting questions I receive a lot of glaze troubleshooting questions and the first question I generally ask in return is "What did your witness cones look like?" This is because knowing whether the kiln was over- or under-fired, and by how much, is important for diagnosing many glaze issues.⁠ ⁠ Sometimes I'm given a kiln temperature in response. But knowing what temperature your kiln reached is only part of the story. Seeing the physical witness cones from your firing gives you a much more accurate description of the physical effect that particular firing had on your clay and glazes.⁠ ⁠ I put at least one cone pack holding 3 witness cones in every single firing. Occasionally, I’ll put a cone pack on each shelf to find out how evenly my kiln is firing. Cones give us a peek into the health of our kiln, before it gives us any real trouble.⁠ ⁠ Pyrometric cones provide valuable information about each firing and it’s really difficult to troubleshoot firing issues without them. You never know when you'll need them until it's too late.⁠ ⁠ In my blog post, Temperature vs Heatwork - Why We Use Witness Cones, I describe the difference between "temperature" and "heatwork" and explain why using witness cones is essential to understanding your glaze results.⁠ You can read the full article via link in my bio.⁠ ⁠ Fun Fact: After publishing this article, I was contacted by Thomas McInnerney from @orton_ceramic_foundation (the makers of our witness cones) who said:⁠ ⁠ "I wanted to thank you on behalf of The Orton Ceramic Foundation for the fine job you did with your blog post “Temperature vs Heatwork - Why we use witness cones.”⁠ ⁠ An official stamp of approval from the cone manufacturers definitely made my day!⁠ ⁠ Do you put witness cones in your firings? If not, it might be time to start, especially if you're not 100% pleased with your glaze results.⁠ ⁠ #kiln #firing #glaze #glazefire #glazeresults #heatwork #kilntemp #ceramics #pottery #witnesscones #conepack #ortoncones #pyrometriccones
When calibrating your kiln sitter, working with a When calibrating your kiln sitter, working with a tiny screwdriver and other small instruments, the last thing you want to do is open Instagram on your phone and scroll through a lengthy post! To make it easy and accessible for your use, I provide a downloadable full colour pdf version of my blog post via the link in my bio. Having this guide on hand to reference as you calibrate your kiln sitter will be helpful. ⁠ ⁠ To review the information and reinforce your learning on this topic, you might also want to watch and listen to my video, "Ceramic Story-time with Sue," where I read the blog post live inside my Facebook group and answered questions viewers had about the kiln sitter and calibration process. The video is embedded right there towards the bottom of the article.⁠ ⁠ I try to make it accessible and welcoming for all. If you haven’t checked out the complete blog post yet, you can find it via the link in my bio, with the downloadable pdf and video versions!⁠ ⁠ #kilnsitter #kiln #manualkiln #electrickiln #kilnlife #studiolife #oldschool #ceramics #pottery
What if you discover, after calibrating your kiln What if you discover, after calibrating your kiln sitter carefully following the guidance in my last post, that your kiln is still not firing accurately? It could be an indication that your sensing rod is worn out (SWIPE LEFT) In this post, I share information to help you determine whether a worn out sensing rod is affecting your kiln’s firing accuracy. After reading, I think you’ll understand how the kiln sitter and sensing rod work together and how normal wear and tear on the rod over many firings can affect your firing results. ⁠ ⁠ Understanding how your kiln sitter works will also enable you to make small adjustments depending on whether you want your kiln to shut off earlier or later. I discuss these steps in detail in my blog post, as well as some important safety considerations. When you make extra adjustments to your kiln sitter, you’re guessing how far to slide the trigger plate up or down. It’s very easy to move it too much, which could mean your kiln won’t shut off at the right time. ⁠ ⁠ Please note: the kiln sitter is NOT a fail-safe method for shutting off your kiln. I strongly recommend being present for the end of your firing to watch your cones fall and ensure your cone sitter doesn’t shut the kiln off too early or too late. Being present for the end of EVERY firing is always the ideal.⁠ ⁠ I share some of my own unexpected experiences with kiln sitter mishaps in my blog post, which you can read following the link in bio. Though unfortunate, these occurrences have strengthened my resolve that it is better to be safe than sorry when firing your kiln, and why I am always present at the end of a firing to make sure the kiln sitter falls and the kiln shuts off. ⁠ ⁠ While the risks of a kiln catching on fire may be low, there is still the risk of your entire kiln load being over-fired, causing your clay to bloat and your glazes to run. Why risk ruining a load of pots that you’ve worked so hard to create?⁠ ⁠ The best way to minimize these risks is to be present and watch the cones melt at the end of the firing. That might mean you have to stay up late, set an alarm for every half hour to go check the kiln. It’s a lot! But it’s important and worth it!⁠
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Recent Posts

  • Glazy Demo – Adding Recipes and More

    Glazy Demo – Adding Recipes and More

  • Why Specific Gravity Isn’t Listed on Glaze Recipes

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    A Potter With a Paycheque?

  • A Clay Reclaim Process Using a Pugmill/Clay Mixer

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