Let's Get Started with Single Firing

[George Lewter]

So, is anyone ready to dive into single firing? I have some bone dry test tiles I'm going to try out with a couple of my glazes that I know shrink a lot on bisqueware. I have a Ron Roy black that I think might make a good raw glaze for dipping to glaze greenware. I'm going to make some small bowls with grippable feet, that I can hang onto when I dip them. I'll try glazing some at leather hard, some at bone dry, and on the last batch, also bone dry, I'll wax the feet and spray them. Hopefully, I can have them done in a week. We learned that waxing the feet is pretty necessary when spraying greenware. The glaze gets under the pot, and if you haven't waxed, when you wipe off the excess glaze, you'll also be wiping away the clay!

[George Lewter]

I fired another load that contained some raw glazed pots, and though the glaze effects were nice, I had some serious body issues. The pots were tumblers like the three shown above and mugs. All had the same Richard Bush Nutmeg glaze as above and an accent glaze of Varigated Slate Blue from Hesselberth. I poured the interiors and dipped the exteriors and poured the accent color around the outside of the rims. It didn't take long until I saw blisters appearing mainly where the pots had been wetted three times. I was able to press the blisters flat but the clay was delaminated and it got worse again in the firing.

As you can see, the blistering was pretty severe, and was present in all the pieces with this glaze combination. There was one blister in one of the mugs where only the Nutmeg glaze was located. It's really puzzling because the three tumblers from the previous firing were fine.

[George Lewter]

Comparison Tests from My Last Kilnload I wanted to try single firing some pieces using the same glazes and compare how they came out versus bisque glazed pots with the same glazes.

These tumblers were glazed the same with C. Harris Temoku (the recipe I have published on this network) with a splash of Light Stormy Blue from the Hesselberth and Roy book Mastering Cone 6 Glazes. Both are on Laguna #80 brown stoneware. One on the left was glazed raw when it was bone dry, the right one had been bisqued to Cone 05.

Two jugs were dipped from the bottom up the sides in C Harris temoku (left one about 2/3 of the way - right one 1/3 of the way. A grey green scrap glaze was sprayed above and lapping over the temoku a bit. On the right jug the scrap glaze was a band with Jens Juicy Fruit sprayed at the top and lapping down over the scrap glaze. THE RIGHT JUG WAS SINGLE FIRED.
The above pieces were all fired in the same load with slow heating up through 1400 degrees F, normal fast as possible rise to cone 5 1/2 tripping off the kiln sitter, half hour hold at 2102, 1 hr hold at 1706, natural cooling from there.

[George Lewter]

George Lewter said:

Now that I've actually had a couple of successful single firings I have to say the assumptions I started with don't really hold up. On Bone dry clay pouring an interior is OK on Laguna #80 and B-Mix 5. Immediately dipping of the exterior on B-Mix has caused my pots to blister on 2 occasions. The little rings on this test cup formed around the blisters that were in a band all the way around the cup.
Waiting a day and spraying the exterior totally eliminated that problem. The problem wasn't as obvious with the #80 brown stoneware, but I haven't tested many pieces that way. My first experiments with dipping leather hard ware were pretty dramatically unsuccessful, so I discontinued that line of experimentation, but it may have just been the glaze was inappropriate.