• Locke

The Great Carbon Trap Research Project - 1

Welcome to what is going to become an ongoing series of blog posts on my year-long carbon trap shino research project!

I'm in the second half of the glaze course offered by Otago Polytech - called Ceramic Finishing. The main thrust of this half of the course is a research project of your own choosing. I have chosen to try and formulate my own carbon trap shino recipe that will work well with the materials and facilities I have access to at the school. I'm also aiming for a smooth, glossy finish as opposed to a crawling or pin-hole filled one.

The first thing I'm doing as part of this research is to test basically as many existing carbon trap shino recipes as I can. Which, right now, is 17. These come primarily from the ubiquitous John Britt book, The Complete Guide to High-Fire Glazes. Some of the recipes are ones found on, and one of them is from our records here at DSA.

To start with, I am testing on Mac's Mud Classic White clay. I know porcelain is the preferred clay for achieving nice carbon trapping, but damn is porcelain expensive! So I must compromise. I also will test with Mac's Mud Whitestone as it is my most-used clay. I've also had good carbon trap results on that clay body in the past, despite many saying that stoneware isn't great for it.

Test cups, freshly glazed!

And so I got into it! Not much to do but put my headphones on, and work my way through mixing up 17 batches of glaze. I made sure to use warm water to help the soda ash dissolve more fully before being sieved through 100# mesh. I got my 17 Classic White test cups labeled and poured/dipped them all on a Thursday afternoon, planning to fire them the coming Tuesday.

In retrospect, I didn't do the best job on this firing as I could have. It went into reduction, sure! But not heavy enough to achieve carbon trapping. I think I was a bit too antsy to get the temp up and toyed with the damper too much, causing the reduction to falter a bit. Not smart! Definitely something I will make sure to work on the next firing.

In addition to the poor firing, I think I needed to let the cups dry longer after being glazed. While four days was enough to really dry out a shino during the summer, the temperature has been dipping and doing weird stuff here in Dunedin this week. I think this meant that the soda ash didn't have the opportunity to reach the surface quite as well.

Here's some of my favorite results, even despite not being what I wanted:

This does mean that my first set of tests essentially... mean nothing. The only one that had a little bit of carbon trapping is the one from our records, that I now call "Reading Error Shino". The recipe is titled RJ Shino, but when compared with the traditional recipe for RJ Shino, I noticed that at some point, someone had accidentally dropped the decimal in the soda ash percentage... changing it from 2.9 to 29! With such a high amount of soda ash in the recipe it's not a wonder that of all of them, that was the one to get some shadowy-ness. It's also the one that as I was taking out of the kiln I immediately dropped and smashed on the ground!

So, even though I didn't get any results I was looking for, it was still a learning process and helped with my research. I've made up a bunch more tester cups - including some Whitestone ones - for the next firing.

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