Let's Talk Organic

Here is the formulation for the nice chrome-tin glaze I posted yesterday. Now we as potters will focus on these recipes. And there are some things to pay attention to on these raw material formulas: First, look for ways to remove soluble ingredients like Gerstley Borate or Colemanite. This glaze has already eliminated those types and replaced them with an insoluble frit. Second you need to have at least 5 to 10% clay component. Fine here. What isn't included in this recipe is the organic components that aid in adhesion, cohesion, viscosity, and anti-foaming agents. So how can this be improved so as to eliminate the crawling experienced in the initial application?

The first focus should be on the addition of a CMC or another organic binder to increase the adhesion of the glaze to the pot and the cohesion of the raw glaze. In addition to that I like a dispersant that reduces the viscosity of the glaze suspension. The best choice here is an ammonium polymethacrylate such as Darvan C. This is the most powerful dispersant available and doesn't introduce another alkali such as sodium which may interact with the flux package. Finally I like to add a silicone defoamer such as Dow DB1410 or other brands. This reduces the amount of bubbles that often end op on the the surface of pots - especially on the lip. So..... Let's tune up the raw glaze with organic additives.

Creepy Crawler

Here's a glaze worth pursuing.  Or rather perfecting. I love the purple color, the satin finish, the way it breaks over edges. What I don't like is the uneven thickness and its tendency to crawl leaving bare clay spots. 

Now this is the project for the next round of firings. Soooo....... What are the causes of these defects?

Let's start with the crawling defect. This can happen in the raw glaze because of drying cracks, dust on the surface, or a drop of oil or wax resist. It can also happen during the early  stages of firing as the carbonates burn out. Zinc oxide, wollastonite or bone ash can contract excessively at high temperature.  High viscosity and surface tension in the melt can also contribute to crawling. 

For the unevenness, the flow behavior of the raw glaze mix has the biggest impact on a uniform application. But again, the high temperature viscosity of the melt will also either help or hinder leveling. 

So.... Stay tuned...  The creepy crawler will be banished at the next glaze session. 

When is 36 Not 36?

We all like to be our own Chemist. We take pride in ordering raw materials and weighing out each powder, mixing and applying, and we glory in the joy of the results. It's magic.

But do you ask enough questions of your raw materials? When you order feldspar or Spodumene is the name all you need to know about it. Try asking your pottery supply house for a certificate of analysis for these raw materials you are buying. This is not easy to get. You should get some verification as to the chemistry AND the particle size distribution. The chart in the picture here is from one of my favorite texts (The Chemistry And Physics of Clay by Grimshaw) and shows how three very different distributions can all be labeled as 36 mesh. The behavior of these three different powders can be very different in your clay body or glaze. It will have an impact on plasticity and on the amount of liquid required for your application. So.... Start asking, paying attention and thinking about it. 

The Magic of Tea and the Discovery of Progress

I find surprising progress as a discovery after years of investment in time and thought. I like the word discover because it more accurately reflects my experience in the advance of my skills and aesthetic. When I was younger I worked hard to master skills in mimicking the pots I respected. Since then I have made a lot of pottery... and I have looked at a lot of pottery. I now don't mimick other pots. Instead I have a general shape in mind and a standard (unwritten and un-articulated) based on the cumulative aesthetic of "good pots" I've absorbed over the years. This week I received a real compliment that couldn't have been planned or elicited. Fukamora Yosi, an engineering manager from our facility in Japan was visiting and I worked all afternoon on Friday with him. late in the day I offered him some tea and made him a cup of green tea in one of my Yunomis. A curious expression came over his face as he asked: "Japanese?" . He become more curious when I told him it was my own. He was pleased and enjoyed his tea as if it was in his own home. It opened up our relationship as we learned about each others family, home, hobbies and interests. The power of Tea.

Finish the Job

Sometimes its best to complete a project and move on. I've had these bisqued pots on my shelf for some time. For a long time I was determined to develop glazes that are right for these pots. But in many ways they occupied valuable shelf space in my shop that needed to be cleared in order to make way for the next round. I finished this and others with a combination of ash, terra sig, some iron saturates, chrome-tin, and strontium saturate glazes designed for cone 6. This vase (23" X 15")  along with a few others will feed ideas for future work. and having cleared out my pile of bisque, I'm ready to start on the next batch.

Gettin back to it.

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Most of my work has been an exploration of vessels; teapots, carafes,
pitchers and vases. The combination of utility with a visually stimulating form and surface challenges me more than other forms of artistic expression where function is detached from beauty. With these vessels I have tried to create a tension between the components of form;
foot, body, lip, handle and spout. In any given pot I look for a dynamic balance between these components that is comfortably tied together by the surface treatment of glaze and design. I work in series and find that the most successful pieces are often not those invested with the
most attention and aspirations. Rather they are often a surprising elevation of a modest piece by the final treatment of glaze and fire.