• More kiln stuff

    A couple of more models came out of the kiln this morning, the own center and the Nortown Theater Art Deco panel Nr D7.

    D7 weighs 38# and it was somewhat of a surprise that the panel weighs pretty much what it weighed before going into the kiln, I had thought the process would continue to burn out materials, the chemically combined water, and that a percentage of the weight would be lost as a result, that seems not to be the case though it may have lost a very small amount of weight the scale wasn’t accurate enough to register, on the order of less than a pound.

    That was good to find out as I now know the final weight for the fired ware will be very close to what the sculptures weighed when bone dry before being fired.

    Shrinkage however is another story, as expected, the firing process results in about a 1/2″ shrinkage per lineal foot, so the D7 panel is around an inch shorter in length than it was.

    Of course this is a known factor and compensated for in overscaling models if a certain size is required in order to fit it something else.

    One could in fact achieve a size reduction in this way by repeating the process, I could take this fired model now, make a plaster mold from it, press clay into the plaster mold and fire that cast and make a silicone mold. The resulting cast-stone casts from that would be consierably reduced in size, but the amount of work involved would be more than simply making a new smaller model.



  • Kiln firing continued

    After several more loads, I now have several of my original sculptures preserved in the hard terracotta state.

    Other than some minor warpage of the JMCCO monogram panel due to it’s tipping forward at an angle in the kiln during the firing process, all the other pieces turned out completely free of any cracks or other issues.

    Here are some photos of the now fired sculptures, all but one was modelled in Continental Clay’s raku clay which can be fired up to cone 10, I fired all of these to cone 1 except the angel panel. The thing is, I never actually intended to kiln fire any of these models since they were generated just to enable taking a silicone mold from, but most of the original models came out of the mold making process intact and so I thought it would be a shame to throw them out and just stored them away on a shelf in the basement. A few of these have been stored away since 2005, 2006. A few others suffered some minor to major damage in the mold making process, the owl center sitting in the kiln as I write this lost a little surface of his beak and the top scroll broke off, the Senator Hotel griffin panel broke in half, but I will fire what will fit, and repair as practical.

    The where is this kiln firing going now is a good subject, it’s been a goal for a considerable length of time to eventually phase out casting anything in concrete for exterior use and restoration or new installation in a brick wall. Replacing the concrete with a more durable, valuable, and historically correct material like terracotta has been part of that goal. The plans have been to develop a small number of models to be able to offer them in this material.

    Most people don’t know a lot about the processes, and it’s too involved to go into detail here, but essentially to make these in terracotta, very complex multi piece plaster molds (instead of silicone and plaster) must be made, and every undercut in the design either accounted for with the mold sections, or temporarily filled in so the hard plaster mold sections can be removed. What that means is, every cast made from clay in these molds will have to be hand refined and detailed to put back any undercut areas that were filled in, and generally clean up the mold seem lines.

    This is exactly how the original ornaments were made in the 1800s, but labor was cheap back then and today I have to consider the cost for firing the kiln and my time hand detailing each piece.

    I determined the kiln takes a little less than $5 worth of electricity to fire to cone 1 over 18 hours 50 minutes (56 kwh on the electric meter) and for the most part I can only fit one, or at most two pieces in at a time, and even though the kiln is automatic, electronic controllers do fail, so every firing will need me to drive over and check to be sure it shut off properly.

    The purchase of the clay and more importantly the shipping costs for it, is another cost to consider that has to be factored into the pricing of these.

    I don’t feel the current economic situation is conductive to marketing this with much success, but working on the firing aspects and possibly experimenting with glazes, and then making a mold for a small piece is a good preliminary start towards offering these later.

    The 202 cherub


    Rear of the cherub 202


    The 649 Pan center


    D5 Art Deco


    JMCCO monogram panel done in Continental Clay “Course Red” clay


  • Firing #2

    Ok, firing #2 went fine, nothing cracked or exploded 🙂

    There was one issue with the monogram panel however, I had it in the kiln on edge resting on 3 posts, but at some point during the firing it tipped forward and leaned one top corner against the brick, as it only had about an inch and a half space it didn’t tip very far, but apparantly it was enough to cause it to warp a little across the opposite corner which was not touching the brick. It’s not a real big deal but I wasn’t thrilled with the warp.

    The photo compares the color of the same clay- angel was fired at cone 05 and the monogram at cone 1, that’s quite a dramatic difference! The red migrates a little more towards brown, a little browner than I expected, I might see what cone 02 would bring out- a little less orange 04 has, with more red and less brown cone 1 has.

    The difference in temperatures between the two is 1945 for the angel and 2079 for the monogram, just 134 degrees difference there makes this dramatic a color difference.

    The male keystone made from the raku clay came out fine, the lacquer on it all burned away leaving no residue of any kind anywhere, so it looks like that’s not a problem, I measured him as green at 20-3/8″ tall, and at cone 1 he shrink almost exactly one inch to 19-3/8. The color is sort of a pale cream, not very interesting but the goal was to just make it permanent so it’s no longer soft easy to damage greenware.

  • Next load

    Now for the 2nd load in the kiln, I was able to fit the 621 male keystone and the monogram plaque. This time I decided to take it to cone 1 @ 2079 degrees which should give the red clay of the monogram a very nice darker and richer red color. I won’t know untill to-morrow night how they turn out as it will take at least 10-12 hours to cool down enough to open the lid.

  • First kiln firing

    The moment of truth was last night, after connecting up the vent I placed my angel model in the kiln on end, it had barely 1/2″ of space between it and the underside of the lid, so it just fit!

    I used the pre-programmed slow bisque setting and let it run.

    About 13 hours and 16 minutes later it reached cone 05 as set to, and shut off. I decided to go and check on it to make sure I had set it right and it worked properly, so I went over at about 5 AM and it had shut off about 40 minutes earlier and had cooled down to about 1685 degrees, so I shut the vent off and went to bed.

    It took about 10 hours to cool down to about 250 degrees, so I just propped open the lid and did some work for a bit and let it cool down to about 170 degrees before I took angel out.

    The model firing came out perfectly, not one crack or any warpage, she shrunk about a 1/2″ in length.

    The color came out like the sample on the left in this photo.

    The model after firing, the heat of the kiln’s 1900 degrees changes the color of the clay to a very attractive red-orange brick color.