Chemistry and Fancy Words
The end of 2015 was quite a wild ride in the studio mostly because of chemistry. At some point in late September things went a bit funny with our dark slip. The unexpected results continued into October and by late October nearly everything we’d made was coming out with big brown spots. I actually love brown, and don’t mind spots, except that it’s not what our wholesale and online customers expect. The chemistry of ceramics is not constant. Clay supplies are dug out of the ground, and materials sometimes shift in composition and character.
So, in the midst of our busy production season, we were faced with a serious chemistry challenge. It was clearly an “application” problem. We spray our slip and my first line of thinking was to look at one of the “suspension agents” in our recipe. “Suspension agent” is one in a long list of fancy words used to describe the materials of ceramic processes. We were most suspicious of an ingredient called “VeeGum T” which is described on one of my favorite materials web sites (www.digitalfire.com) as: “a complex colloidal and extremely plastic and sticky magnesium aluminum silicate.” Back in my earliest days of ceramics education this chemistry jargon could make me twitch..or make a joke (which I tend to do frequently). In undergraduate school, we used to say our friend had a tendency to “flocculate” at parties. Coffee was often recommended as a “deflocculant.” I will leave it to the reader to discover the definition of that fancy word. In the days when I first learned about it, there was this thing called a “dictionary” we had to actually open and turn pages to use. Discovering definitions has gotten easier in this millennium.
After many years of dealing with ceramics materials, I now have great appreciation for some of the chemistry fancy words. So here’s one that has always been a favorite: thixotropic. What a great word. I like to say it just to have it roll off my tongue. Unfortunately, part of our recent problem was that our slip was appearing thixotropic. Thixotropic is defined as: The property exhibited by certain gels of becoming fluid when stirred or shaken and returning to the semisolid state upon standing. The way I most frequently think of “thixotropic” is like taffy that appears as liquid when it’s not being agitated. It sounds cool, and it really is…except that it is too sticky to spray.
In looking at our use of VeeGum T, I discovered a couple of interesting facts. We have been mixing it into our slip utterly against the manufacturer’s recommendations, and using it in about roughly double the recommended amount (the result of a calculating error committed about two decades ago). While surprising, I didn’t really think this was causing the problem, because we had been doing it for decades (good news for our clay supplier who has been selling us twice as much as we probably needed for many years now!). Still, in looking at the problem, I discovered something that one would think might cause a problem but didn’t. In the meantime, it occurred to Anna (my incredibly astute assistant) that we also happened to be working off a fairly new batch of synthetic Albany Slip. That’s not generally an ingredient that one would suspect of influencing application, but it was really the only thing that had changed.
Our clay supplier figured it out as soon as I told him the slip seemed thixotropic. That one word made him say, “Aha.” They had gotten a contaminated batch of feldspar but weren’t sure exactly who had been affected by it. “Thixotropic” was the word that seemed to clinch it. He offered to replace the effected slip at no charge and I was happy to accept that. While I felt kind of bad about our pile of seconds, I felt worse for them, imagining the several tons of clay they mixed that went thixotropic…while I might sort of like to see that, I am mortified at the magnitude of it.
Prior to pinpointing our problem, I came up with a workaround which involved Epsom Salts. Epsom Salts, while not a fancy-sounding material, can be used in glazes and slips to temporarily thicken them. It also seemed to combat the thixotropic problem temporarily so we could spray in the right consistency. I have fond memories of my ceramics professor at Edinboro University of Pennsylvania, Donna Nicholas, searching around the glaze room for the Epsom Salts (ceramics 101 students tend to over-thin the class glazes with great frequency). Unfortunately, Epsom Salts is water soluble which creates a kind of roller coaster of too thick and too thin so it wasn't a permanent solution. I would say the last three months of 2015 were pretty similar to an arduous roller coaster ride. The low was the day I unloaded two kilns with only about four (out of roughly, 100) pieces that were acceptable. The high point was opening two kilns just after we managed to figure the temporary solution, and realizing there were only two pieces that I would not call virtually perfect. It felt like a Christmas miracle.
Do you like spotty brown plates? Are you interested in some really good prices? There will be a LOT of work just like that (especially in the “moon and star” pattern—which was the bulk of my wholesale order)on the seconds table at my next few Open Studio sales. Come on over to Kaleidoscope Pottery’s crazy bargain seconds table, and take advantage of the “Thixotropic Slip Debacle” of 2015. Next opportunity is our “Winter Warmer Artisan’s Sale” on Saturday, February 13. See our web site for details (and do note, we will also have plenty of first quality work to compliment the seconds!). Mention the word “thixotropic” and I will be really impressed.
5/30/2022 03:25:58 pm
Can't decide whether you are awesome pottery maker of storyteller. I enjoyed that article very much!
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Evelyn Snyder, Potter