Research

It seems I'm always doing research. I've been reading a lot about matte glazes, in trying to get something in a cone 6 matte. I've run into a clay club blog with some good glazes on it. It's amazing how you know when you find good websites or blogs, and then you run across them referenced on other websites and blogs. In this spirit here are some links I find fascinating.

http://www.patrickhorsley.com/

http://www.kazegamas.com/index.htm

http://ncclayclub.blogspot.com/

Etsy

You can now see on the right side of my blog a gallery listing from my Etsy store where my pots can be viewed and purchased. If you would like more information, or to put in a special order request please email me at potterpdx@yahoo.com and put "BenCo pottery questions "BenCo pottery special order" in the subject field.

Glaze Research

Digital Fire has a lot of free links that hold a wealth of information. You can find chemical data on nearly all individual materials, as well as a number of formulated glaze recipes. What I've been working on the last week is trying to figure out proper formulations for durable matte glazes in both Cone 1 and Cone 6. I have found a myriad of recipes for high gerstley borate matte glazes. Which I know from first hand experience from testing in college that these glazes are not durable and they leach. So I'm trying to come up with a formula made from the materials I have on hand that make a matte glaze. The good news is I've found shiny base glazes for both the cone 1 and the cone 6. I've also found some proven cone 1 and cone 6 macro crystalline glazes. I have a lot of testing to do now that I've done some research. However for anyone who might be interested in these types of glazes here are some links to digital fire that might help.

http://digitalfire.us/4sight/education/g1214w_cone_6_transparent_base_glaze_121.html

http://digitalfire.us/4sight/education/g1214z_cone_6_matte_base_glaze_122.html

http://digitalfire.us/4sight/education/formulating_ash_and_native-material_glazes_188.html

All three of these links are great. The last one is of particular interest because I have an ash deposit that contains a known material cataloged by a geologist with the USGS.

Good in Bad

You know how they say things happen for a reason. Well this recent firing made me read up on a lot of stuff I'd already learned but had maybe not remembered lately. It also made me do a bit more digging to find some things I did not know.

For some time now I've been interested in doing crystalline glazing in my studio. In fact it was Wally Schwab who first introduced me to crystalline glazes when I studied under him at PCC Rock Creek. I'd also done quite a lot of research into microcrystalline glazes at MHCC with Don Sprague. Since then some advances have been made by other potters to fire these glazes at cone 6. When I looked at these before I'd found a cone 1 crystalline glaze as well, but had lost the recipe. Well I found it yesterday, so I'll be tinkering with that one soon thanks to Charlie Cummings post on Clay Art Thread. I also did some research into the firing schedules and found out that the crystallization is happening upon cooling, but a very slow cooling where the kiln is held at the 1830 - 1900 degree mark for four hours. What's interesting is this is when the iron in cone 5 iron reds is held to facilitate crystallization as well.

As you may know there is a huge difference between Orton cones. The large ones drop much faster than the small ones, in fact a large cone 6 drops at 2228 where a small doesn't drop until 2291. Sixty three degrees doesn't seem like a lot when you're talking about thousands of degrees, but it's enough that it could make a glaze go from stable to runny. It's not just the temperature but also the time it takes to get to the higher temperature.

Charlie Cummings
Macrocrystalline Cone 1
Frit 3110 - 43
Zinc Oxide - 23
Silica - 16
Lithium - 9
Laguna Borate - 9

Firing Up, Firing Down

After doing a lot of reading over the last several days. I think I've found the answer to the glaze firing problem I had recently. The potters who fire reds fire up and then ramp back down slowly. Some shut the kiln down and then manually hold the setter back on for 20 minutes in the 1800 - 1900 range to allow the crystallization of the iron molecules that reflect the color red. This is where Crystalline glazes also ramp down to and hold for a number of hours. Some potters however who were doing reds actually fired back down slowly to achieve the red coloration. This is also used to more slowly cool a kiln to allow a glaze to stop bubbling and heal over. In my case the cone malfunctioned and I did not have witness cones inside (big mistake) to tell me when I'd reached peak temperature. I've decided to do my glaze firings based on witness cones instead of relying on the setter to shut it down. This way I can fire back down slowly cooling the glaze.

Misfire

After some consideration I'm fairly certain that my trouble with this firing was a cone malfunction combined with a quick cooling. I did a leak test on some cone 10 pots I put in the firing and they are vitrified. Some parts were unglazed and did not leak. The cone 6 glazes I used were supposed to be matte and completely melted and ran down the pots. The kiln took a very long time to reach top temperature, like 4 - 6 hours longer than I expected. I'm fairly certain that the kiln actually hit cone 8 - 10 range. I'm going to purchase a packet of cone 5 and a new box of cone 6 and try these glazes again.

Lack of success

Well my first cone 6 firing in my new location was a failure. The kiln cooled too quickly trapping bubbles in the glaze on all the pots. The matte transparent also came out a shiny and clear which leads me to believe that the long time the kiln took to reach temperature made the glaze over mature. It became fluid and started to run down the pot as if it were not a matte glaze at all. Quite disappointed in this one, however I did get some great color response in both the purple and the blue. As Churchill said "You can always count on American's to do the right thing, after they've tried everything else." Looks like I need to wrap my kiln is fiber or something.