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 glazy.org, 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.
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.