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A Review: Matt Katz’s "Introduction to Clay Bodies" Online Class

Ceramics class Clay Body Formulation Matt Katz Online class for potters Pottery Class

Part One: Preamble    One of the few economic laws you can depend on is this: being cheap always ends up being expensive. And, if you are making some or all of your income from making pottery, you have probably learned that there are no short cuts.

Somebody forgot to get that memo out the the companies who make clay for potters. Over the years I have suffered from poorly made clay, and if you have been making pottery for any length of time the odds are that you have as well. I believe that the majority of clay companies in the United States are guilty of using the lowest cost raw materials, and then to save further, they don't mix the clay properly. Often, the clay recipe is not properly formulated. Clay companies sometimes will make a cone 10 clay body and sell it as both a cone 10 and a cone 6 clay without making any adjustments to the formula for cone 6. Meaning that they are selling a cone 6 clay that only matures or fires properly at cone 10! The odds are high that you have had to put up with bad clay, and had to adjust your forming techniques suit the clay's temperament. The end result of this can be a high percentage of unsaleable pots, or spending much too much time on a pot in the forming and firing stage in order to get marketable ware. Further, you may not even know that you are putting up with this situation, for you may have been told “that’s just the way it is with clay” and you believed whoever told you that. 

I could write a whole blog post speculating on why clay companies do what they do, but I’ll spare you. Briefly, it seems to me that most clay companies have one major customer, schools. In order to compete to get orders from schools, the clay has to be cheap. In order to make clay cheaply, the material costs have to be as low as possible. And the time required to make the clay has to be minimal. Clay making equipment costs have to be held as low as possible. So, what you end up with, more often than not, is clay that does not perform properly or consistently over time. Headaches ensue for potters. It sure seems like the clay companies are making a product that is “just good enough” rather than “excellent”. My theory is that the educational customers probably rarely or never complain about bad clay, and the professional or hobby potters who have had problems with the same clay are often told with a straight face, “Weird. You’re the first person who’s had a complaint with that clay." I've heard that there have been Facebook postings by ten or more potters complaining about a bad batch of clay made by a certain company saying "That's what the clay company told me about that clay too. Now I know it's bad clay, not my kiln. And I know I'm not the only one!! Why did they lie to me?" Most of these companies are notorious for blaming the potter for doing something that is causing the problem instead of admitting that they screwed up. This has been my experience and also what I have heard on more than one occasion from other potters who have told me their clay horror stories. 

Before I get in to my review of Matt’s class, let me just state this. I wish the clay companies did a better job. I wish that at least one of the companies in the States would make a line of premium clays that are well formulated and well mixed. I would happily pay double for my clay. Happily. It is negligible to me to pay an extra fifty cents for the clay used to make a mug when my customer is paying thirty to fifty dollars for the finished product. That is cheap insurance and would save me days of work every year, not having to remake an order that did not come out properly due to flaws in the clay. Please understand, I’m not anti clay company. However I am anti crap clay company, and I would be thrilled if some enterprising potter started a company that catered to excellent, consistent clay production. I believe that there is a market for such a product. Okay, enough of my rant - let's get to the review!

bloatingiron melt out

The photos above show some really shitty clay. The bloating was blamed on the potter by the clay company. She fired to cone 5, they said "Oh, you have a Skutt kiln, they fire two cones higher. She had a witness cone that showed cone 5. And they want repeat business? The iron melt out in the tan/green mug was blamed on the potter's kiln burners until the potter (in this case, me) found chunks of iron in some of the bags of clay. The photo with the ruler shows big agglomorates of bentonite. In spite of this the clay company insists that the clay is in fact mixed properly. I need an aspirin. Sigh.

Part Two: My Review   There are a ton of books out there which teach glaze formulation. Some are good, a lot are mediocre, and some are really bad. But, you cannot deny the fact that there are a lot of books about glazes available to the potter. 

The same is not true of books about clay bodies - at least in my experience. So far as I know, there is not a book out there devoted solely to clay formulation and clay making techniques that is written in a way that mostly non-scientifically minded potters such as myself can understand. Yes, there are books out there with chapters in them about clay, and there have been some articles written on the topic for the various ceramic publications. But when I read them, I've never really been able to understand them. There didn’t seem to be a source providing the basic building blocks of information that I sought so that I could begin to learn about clay. And so, although I’ve had a desire to learn how to make my own clay body for many years, I felt stuck, and felt that I might never be able to understand the mysteries of clay and clay making unless I went to great expense to enroll in a really good ceramic program at a college. The cost of moving, having no income while at school, cost of tuition, rent...sorry, but this is just not a realistic option for me at this stage in my life. 

Enter Matt Katz. I'd heard about Matt’s online classes several years ago. At that time, his classes were only available through Alfred University in upstate New York, and they were spendy. And at the time, Matt was focusing on glaze classes. I was really tempted to enroll, but in the end there was no way I could afford the tuition. Some time in the last year or two, Matt, along with his wife Rose, started their own online learning center at They are now offering several online classes for potters, and best of all, the classes are much more affordable. Yay net neutrality! Late in the summer of 2017, I found out that Matt was offering a new class called Introduction to Clay and Clay Bodies, and I thought, hmmm. This could be my chance. 

Matt Katz and his wife Rose are both clay scientists, both having extensive academic backgrounds in clay and glazes and ceramic chemistry. Matt spent time as a studio potter and then went into teaching at the college level, while Rose spent a big chunk of her career working for really big commercial tile making operations in the US. They both are clay and glaze nerds, which turns out to be an absolutely fantastic boon for the ceramics community.

The timing for the class was the absolute worst time for me, as it started in October and ended in December. These are the absolutely busiest months of the year for me in my studio. I signed up anyways, after much internal debate, the main reason being, what if they don’t get enough people to sign up, and they never offer this class again? That’s just my catastrophic thinking brain at play, of course…but it was a good enough motivation for me to take the class. And what a great decision that has turned out to be! In spite of the fact that I think I had to miss out for a month (I caught up later, when I finished the annual fall/early winter mug making marathon). The class features a library of video lectures presented by Matt that can be viewed as many times as one desires on demand. Each week a new lecture video was posted, and through the class discussion board we were able to ask questions, post our test results, and help each other out. (Side note, you meet fantastic potters from all over the world who are also taking the class - my class had students from the United States, Canada, Denmark and Australia.) Every two weeks, Matt was available for an online “hangout” where we would spend up to two hours talking about clay informally using Google Chat. Matt is a genuinely knowledgeable and fun guy, and it was fun to hang out with him. I should clarify also that it is my understanding that this course will be offered several times a year, check the website for details.

I cannot say enough in regards to how amazing this class was. Let’s face it, we potters who buy our clay from the clay companies never know what is in the clay. The company will never tell us. Even worse, they rarely tell us if they have changed the recipe. For example, I recently found out that the clay I’m currently using has a different flux in it than it used to. Knowing that they changed the flux they helped me understand why the clay that I am recycling is “short”, which started happening a year or two ago. (Look at the cracking in the handle in the photo below.) My reclaim often sits in a bucket with lots of water for several weeks before it is processed, and I learned from Matt’s class that if a clay is fluxed with a high sodium spar the sodium can leach out in water, causing the clay particles to resist sticking together much like a magnet will resist sticking to another magnet when the same poles are facing each other. That is caused by the flux being changed. The only reason I found out from my clay company that they changed from a potassium flux to sodium flux is that I learned from Matt’s class what might be going on, and I asked them a specific question. And, they confirmed my suspicions, which actually was really good of them to do. But I doubt I would have found out if I hadn’t taken this class and did not know what to ask. Of course, when they made the change, they didn't bother to tell me.

Introduction to Clay Bodies is a full-on university level course. In addition to 12 lectures that range in length from an hour and half to two hours, there are four labs assigned that guide students in making their own clay bodies. With Matt’s help, we designed a triaxial test to make ten different test clays, based on the type of clay we wanted to develop. Then, we took the best three of those clays from the first round, and did a second triaxial test using the three best clays from Lab One as corner points for Lab Two to further refine our recipe. In the process of making these twenty clay bodies, we observed how well they work in the studio and how they perform in our kiln. We were also provided with several test methods to determine the clay’s green packing density, fired density, shrinkage and absorption. Along the way we started to learn that most of the clay bodies on the market are just not very good. We learned about certain critical benchmarks that determine a good clay, and looking at some of the stats published on the claymakers' websites will give you a very good idea about that particular clay's suitability for your purposes before you buy it and spend time testing it. For example, we learned that cone 6 or cone 10 clays that have an absorption of over half a percent are flawed clays. (You’d be surprised if you look at data pages from clay companies listing so many clay bodies with really high absorption numbers. You may not have a clue what those numbers mean, but you will if you take this class.) How do Matt and Rose know that clays with over a half percent absorption are not good clays? Science. Testing. Research. This is not a “well, it’s always been done this way, so it must be okay” kind of class. Expect some of your preconceptions and firmly held beliefs on clays to be challenged when you take this class!

I cannot possibly tell you even a tiny bit of what I learned in the class in this short review because this class is so densely packed with information. We learned about ceramic history, geology, types of clay, clay chemistry, fluxes, flint, fillers, clay working techniques, clay flaws and how to fix them, two lectures on what is happening to the clay when it is firing, and a discussion about dispersants, when to use them and why. Oh, and Matt provides no less than half a dozen Excel calculators for use in clay testing and clay evaluation that in and of themselves are worth the price of tuition. (I’m a mac guy, and the calculators work perfectly in Numbers - nice!) And there is an excellent set of articles and white papers that are provided with each lecture, I am guessing there are several hundred pages in all, and even more than that when you add in the class notes that are generously provided at the end of the class.

Is there anything I am missing? Tons. Matt teaches that the main problem with commercial clays is that they simply are not properly mixed. And he teaches us how to mix our own clay better than those guys do, in our own studios. We learn that commercial ceramics suppliers often don’t mix their clays the right way simply because in order to survive in that low cost school market space, they need to cut corners, which I talked about at the beginning of this blog post. It is interesting to contrast this practice to the commercial tile, dinnerware, and sanitary ware companies who actually do spend the money to mix their well formulated clay bodies  properly. Mixing clay properly, while much more expensive, is way more profitable in the long run for these industries because they cut their losses dramatically.

By taking Matt’s class, I've become empowered. I plan to start mixing my own clay in the coming months, once I get my recipe dialed in. By doing so, I will have way more control over my clay and my pottery. In fact, if you make your own clay, you can adjust the clay body recipe to fix glaze flaws. This is something you really can't do if you buy commercial clay, as you can never have the recipe. Having taken the class, and having put in the time to study and do the labs, I can say with confidence: I can do this, and do it way better than the clay companies have been doing it. It’s not that the clay I have been using is horrible. It’s just that it could be so much better, and great clay to me means more profits due to reducing the number of flawed mugs that come out of my kiln that are directly attributable to “just okay” clay. Time is money. Period. Remaking pots is losing money. Period.

This course is highly, highly recommended. I learned so much that even though I feel fairly confident with glazes and glaze chemistry, I plan to take Matt’s glaze classes this year. I have a feeling that I will learn a trick or ten and probably end up having more fun with clay and glazes and making more money as a result.

[Update 1/9/18] After spending some time over several days writing this review, I posted it yesterday. This morning it occurred to me that I needed to add some photos as well as this note: If you are a potter and you do not have any intention of ever mixing your own clay, I still strongly encourage you to take this class, for you will learn many things that will make your life as a potter much, much easier. Trust me! And I also forgot to mention the instructions Matt gave us to make Stick Up will never have to score pieces before you join them together with this magical substance!

Disclosure: This review has not been paid for, nor have I been compensated for it any way. I paid full price for the class. This review is my honest assessment. I wrote this review out of a genuine desire to help fellow potters become better informed on how to reach a new level with their work. And, if this article inspires a clay company or two to "make clay great again" that would be better than excellent! Happy potting everyone! Cheers, Owen 

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  • Peter on

    Hi Owen,

    Really interesting review. Clay should be something that we potters think about, but it is all too easy to buy it by the bag and just use it without understanding it. If it works for us, we are happy, and if it doesn’t we grumble, but don’t know how to make it better! It is funny how glazes tend to get the attention, but the clay gets taken for granted!

    I am starting to think a bit more about clay myself, especially since getting a good de-airing pugmill. Being able to prepare larger quantities of clay more easily really makes it easier to experiment with blending clays. When time permits, I would like to try making a clay body or two of my own. It would be very rewarding to have control over that part of the process.

    Thank you so much for letting me know about your review. I will make sure that there is a link to your site from my blog.

    Best Wishes,

    Peter from New Zealand

  • Lisa on

    The slaking now makes sense too!

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