Sunday, January 29, 2006


Bought a piece of another kiln today, just the floor and one tier of a ten sided kiln.

Its larger than the intended raku kiln, but I plan to reduce the diameter by cutting the kiln brick, and re-bending the steel collar around it, and to use it for the firebox of the raku kiln.

We got another fifty pounds of raku clay, fifty pounds of a cone six porcelain for Julie, and a bag of a locally mined clay, that has a yellowish cast.

Saturday, January 21, 2006

Another Kiln

We bought a used kiln today, from a nice couple, Pat and Marian. They are getting married in the spring, and are working to establish an endangered butterfly sanctuary.

The kiln is a Sno Industries P22, which has an interior that measures 18 inches across and 22 inches deep. The interior cross section is an octagon, with two and a half inch thick kiln brick. It has an analog pyrometer, and a kiln sitter with timer. The kiln was advertised as needing some work, since one of the rotary switches is broken, and the interior tube of the cone sitter is heavily chipped where the blades hold the pyrometric cone, and the blades are missing.

We plan to pull the kiln sitter and heating elements out, and convert it into a raku kiln. We'll have a base of cinderblock on sand, on top of which I'll build a firebox out of soft kiln brick. I'll cut out the bottom of the kiln, and vent hole in the lid, and then place the kiln on the firebox.

The kiln sitter is a later model than the one on Figaro, and it has a safety timer as well as the cone latch. The new model has a larger footprint than the old, but I'm thinking of retrofitting the other kiln with it. I shold be able to use the tube and latch components from Figaro's old sitter, and then use the facing and switches from the newer sitter.

Wednesday, January 18, 2006

New Pictures Up

I posted some new pictures to my Flickr account.

Tuesday, January 17, 2006

Together in the Studio

On Sunday, Julie and I were both in the studio. I sat at the wheel, trimming my mugs, the 306 vase that I had thrown for her, and my dip warmer. Julie improvised a worktable on top of our stack of clay boxes, to work on her dragons.

It was a comfortable arrangement, and we got to chat while working. I used our clay extruder (a cross between a heavy-duty caulking gun and a Playdough Fun Factory) to make handles. After I finished the mugs and dip warmer, I wrapped everything in plastic, and put it back in the damp box to allow the mositure to even out in each piece.

We are planning on another bisque firing by this weekend, and hopefully do a cone six glaze firing soon after. A cone four firing will also need to take place for all of the Cassius Basaltic pieces (Cassius Basaltic will 'bloat' at cone six).

We also have our eye on another used kiln to turn into a raku kiln, rather than sacrificing Bubbles. This other kiln has electrical problems, but we would gut the remaining wiring for its new task. Bubbles would either go up for sale to fund the raku kiln, or be mothballed for future projects (like reworking the heating element controls to use for crystalline glazes).

Julie was in the studio, yesterday, working on dragon vases. She learns more every time that she makes a piece, so her technique is evolving. After the Golden Globes were over, I popped into the studio for a few minutes to trim the small mixing bowl that I made from 306.

Saturday, January 14, 2006

Spoke with Vicki About Glazes

I finally had a chance to talk with Vicki, my pottery instructor down in Atlanta about our glaze and raku woes.

We first verified that the Floating Blue recipe that I have is correct. It in an old composition book, and one of the components of the recipe was added in a different color ink than the rest. It turns out that the recipe was spot on.

From the description that I gave her, she is guessing that the Floating Blue was overfired. This could be caused by turning the kiln up too fast; the rate at which the temperature increased in the kiln at full power caused the temperature to soar past cone 6, before the cone had a chance to bend.

Our kiln has three banks of kiln elements, and each has a rotary switch with Off-Lo-Med-Hi settings. According to our kiln log, we went from all of the dials at Lo to Medium, and then an hour later moved them all to Hi. Next time, we plan to turn the knobs to high one at a time, so will go from all medium to all high in three hours instead of one hour.

A pyrometer would help as well. We never found the one that I bought with the gas kiln, its in a box someplace, but we were thinking of acquiring a digital pyrometer for raku firing.

Vicki also agrees with me that firing the raku kiln in reduction was a bad idea for our glazes.

Post 53 - Busy Day with Clay

Went into the studio this morning.

We are running short of raku clay and 266 (Chocolate Brown). We have a few hundred pounds of Standard Clay 306 (Brown), a box of Standard Clay 308 (Brooklyn Red), a box and a half of Cassius Basaltic, and some dried out porcelain.

I threw three mugs and a large dip warmer (bowl and base) out of 266. I set a piece aside to make handles with, then wrapped the remaining eight pounds or so for Julie, so she could do some slab work. I listened to Barenaked Ladies, their "Gordon" album.

Next, I broke out a bag of the 306. It feels softer than the 266, and in the wet state is a darker color (266 looks like a reddish milk chocolate color when you throw with it, and fires to bittersweet. 306 looks the color of chocolate milk made with syrup, when there is a lot of chocolate in it, and I believe it fires to a toasty buff color with dark speckles. The wet 306 is a bit lighter than Cassius when wet). I threw Julie a tall vase for her dragon work, and then threw a small mixing bowl. It didn't start as a small mixing bowl, it started as a cookie jar, but the rim wouldn't behave when I tried to notch the step for the lid (again).

I put my wet pieces into the damp box, rearranging some drying pieces onto common boards to free up space. Cleaned up all the wet clay and splatters around the wheel, cleaned my throwing tools, then sat down to trim the two Cassius vases that I threw a few days ago.

Julie asked if there was somthing that I could do about the trimming marks, since her handbuilding changes the surface of the piece, she ends up having to play with the whole surface of the vase so the transition from thrown trimming marks to handbuilt dragons is not as noticable. Once I trimmed the pieces, I used a wooden rib to burnish the surface of the pots while they were turning on the wheel, and then ran a wet elephant ear sponge over the surface as well.

Hopefully, the pieces that I threw this morning will be ready to trim tonight or tomorrow.

Thursday, January 12, 2006

Catching Up

Bubbles drew too much power on our garage GFI circuit (needed 18 amps), had kept trippling th e breaker. Julie ran an extension cord from the laundry room, through the door to the garage, and to the kiln. Bubbles never got to cone six. We fired her for almost a day. We were afraid to let her fire for another night, especially with an extension cord going through the door. The next day, we found that the glazes had partially melted, and the cone had just started to bend.

The glazes didn't do what they were supposed to. The clear looked like the icing on a glazed donut, and the matte clear had a really rough surface.

We fired Figaro, the mid-sized electric kiln, to cone six the same day we opened Bubbles. The floating blue turned out such a dark blue that it was almost black. I'll post some pictures of the finished pieces.

I started to read my glaze book, from cover to cover, at this point.

About a week ago, I had half of the nail on my right big toe removed. It hurt, and I've been hobbling around.

Julie has made some more wonderful dragon pieces. Again, I need to post pictures.

I threw two Cassius Basaltic vases for Julie tonight. I was cleaning up my tools to change clays, when Steph entered the studio, and we started talking pottery. I demonstrated the difference between bisqueware and vitrified high fired pieces by teaching her the tongue test. We chatted for a while, then I had to bring her upstairs to go to bed.

Julie has suggested that, since Bubbles takes too long to fire to cone six, and Figaro fires so quickly, that maybe we could convert Bubbles into a raku kiln. We would need to buy a raku burner, and then modify Bubbles by cutting a few holes, and building a fire box out of kiln brick.

Tuesday, January 03, 2006

Meanwhile, Back in the Studio...

I set up 'Bubbles', the small test kiln, for Julie to run some cone six glaze tests. I also mixed up a test batch of a clear matte glaze. She has a small bowl, thrown with Standard Clay 266, that she plans to glaze with Floating Blue, our clear glaze, and the clear matte glaze.

Calcium Oxide and Magnesium Oxide

I've run two raku glaze bases, known to have problems with chromium-tin mason stains, through my glaze calculator software.

Louden's Base contains 22.8% calcium oxide, and 3.79% magnesium oxide.

A base used by Rebecca Johnson, of Buck, Snort and Run Clayworks, contains 24% calcium oxide, and 4.17% magnesium oxide.

According to the Masoncolor site, the chromium-tin mason stains should contain between 6.7 and 8.4 percent calcium oxide, and be free of zinc oxide and magnesium oxide.

On Mason Stains

Did a little research on Mason stains during lunch today, which mainly involved going to the Mason Color web site and trying to identify clues to what happened last week during the raku firing.

The first realization was that the page showing the pinks and crimsons does not include the Tangerine or Lobster stains that seemed to work in the "Louden's Base". The Sunset stain, the one that lead us to using Mason stains in the first place, wasn't there either.

It turns out that there is a separate tab for Encapsulated Zirconium, Cadmium, and Selenium stains. Tangerine, Lobster, and Sunset all appear on this tab. Chemically, they are treated differently than the Dark Crimson, which is a chromium/tin stain.

I also found out that Cornwall Stone, which makes up twenty percent of the base glaze, fires light green in the right conditions. I now believe that the Dark Crimson mason stain turned transparent during firing, due to one of four possible causes:

  1. overfiring (unlikely, since the Dark Crimson stain can go up to 2000 degrees F, and the pyrometer read 1830 degrees max).
  2. the presence of zinc in the glaze, which chemically bound with the stain (unlikely, since I can't find any reports of Gerstley Borate and Cornwall Stone containing zinc)
  3. the amount of magnesium oxide in the glaze (about three percent) bound with the tin and chromium in the mason stain
  4. the reduction firing of the kiln somehow caused a chemical reaction that bound the tin and chromium of the Mason stain

Sunday, January 01, 2006

New Year's Meal

I cooked our New Year's dinner today.

I made two Peking ducks with pancakes, a stir fry of brocolli, water chestnuts, bamboo shoots and baby corn in black bean sauce, chicken pad thai, and sweet potatoes cooked in coconut milk. We also brewed some thai iced tea.

There are four steps in making Peking duck. After it is washed and cleaned, the cavity of the duck is rubbed with a mixture of spices, sugar, and salt, and then pinned shut. The duck is then hung from a knob on a kitchen cabinet, and boiling water is ladeled over the duck, and allowed to fall into a large bowl. The hot water in the bowl is ladeled over the duck for several minutes, and then the duck is allowed to dry for fifteen minutes. A syrup is made from hot water, malt sugar, red vinegar, and lemon slices, and then this too is ladeled repeatedly over the duck. The duck is allowed to dry for at least three hours, and then placed in a roasting pan into a four hundred degree oven for twenty minutes, then cooked at three seventy-five for twenty-five minutes a pound. It is removed from the oven and carved. The duck meat is eaten on a peking pancake, with a bit of duck skin, a bit of scallion, and hoisin sauce.