“Mini-kilns” – Even Better

How didn’t I think of this before? If the little boxes were made out of the same material as the kiln….

For those of you who haven’t read my last posting, called “Little Boxes,” the idea is to improve the firing results by isolating the pieces from each other. Making a small box for each piece prevents heat from flowing from one piece to another, or as some of you prefer to phrase it, preventing the firing box from acting as a “heat sink.” This way, every piece has its own space and none of them interferes with the sintering of any of the others. Those boxes were made of fiber paper.

My new boxes are made from kiln bricks, creating “mini-kilns.” They are not as easy to make as the fiber paper boxes, but if you put a few hours into it, you will have durable, long-lasting, reliable firing boxes that you can use over and over.

I bought a soft fire brick at a local ceramic store. It cost me $4. It’s important to get a soft one. One brick is enough to make boxes for one kiln. You can make boxes of various sizes.

How to make the boxes

Use a pencil to mark the size of the box you want to make.

Using a jeweler’s saw or any other saw, cut the brick along the pencil mark. It cuts almost like butter.

You can lay the cutout part on its side – it will still be tall enough to make a firing box.

Then cut that one in half. Each of the halves will make a box big enough for a 1″ piece.

These are different grinding stones that you can use to carve out the inside of the brick. They usually come as attachments for rotary tools and can be purchased individually at hardware stores.

Mark the inside measurements of the box. The walls can be as thin as ½” or even less.

With the grinding wheel mounted on a rotary tool, start a pilot hole at the center of the brick. You will find it surprisingly easy and quick. There will be a lot of dust. Be sure to wear a mask and goggles.

Continue drilling, going both deeper and sideways, until you reach the pencil marks.

How can you tell when you’ve drilled deep enough? I left the bottom of the box about ½” thick. Measure the height of the box. Then put the ruler inside the box to see how deep it is.

16

Here are more boxes in different stages of preparation.

If you have a drill press, the process will be even faster. Just hold the box in your hands and move it around until the hole reaches the desired depth and the pencil marks.

11

Here are the boxes arranged in the kiln. The are elevated on posts. The two in the front are a little separated because this is where the thermocouple is located.

12

Fill them with ½” carbon.

13

Put in your pieces. Most of these are mixed copper/bronze pieces. The one on the top left is hollow. The box on the bottom left has two pieces. There are also two boxes in the center of the kiln.

Mini kilns 025

Cover the pieces with more carbon.

Every piece, including those in the center, sintered. In fact, some felt like they were over-heated, so in my next firing I am going to fill the boxes with carbon all the way to the top.

Some kilns tend to consume more carbon than others. If you see a considerable amount of ash after firing, or if the pieces get exposed to air, cover the boxes loosely with fiber paper.


34 Responses to ““Mini-kilns” – Even Better”

  • Melody Pierson Says:

    Hi,
    I think this must be a wonderful way to create a kiln. However, doesn’t a kiln need a top? Where does the source of heat come from and will I need a hole to put in a thermometre ? Sorry,I am a newbie to this world of kiln…
    Could you fill in some blanks? I will also re-read this a few more times.
    Thank you, Hadar.

  • Christine Says:

    I was bummed when I did not have any thick fiber paper for the last ones, so I used fiber blanket and a stapler. I worked pretty well, but I think I need to make some of these.

    On thing I am noticing is that the carbon cannot be re-used like it can be with a stainless steel box. It is essentially all burned up with each firing. Is there any way to conserve the carbon?

  • Linda Gaughran Says:

    Hadar, it’s fascinating to watch the firing box evolve. As I was looking at the new little kiln brick boxes I remembered hearing about someone using laboratory porcelain crucible dishes as firing dishes for firing silver metal clay with vermiculite support. They are about the right size(s) for individual firing boxes and they are inexpensive. Do you think they would work just as well for firing the base metals using carbon instead of the vermiculite?

  • Mary Ann Says:

    What an awesone idea! Thank you for sharing it. You know, if you cut a slice of the brick about the same thickness as the walls, you could make lids to put over them when you fire. Would that help with the carbon issue?

  • Jen Garvis-Elliott Says:

    Hadar, genius once again! This will solve my 4″ kiln chamber problem once and for all! I’ve been trying to find mini firing vessels, and now I’ve got a permanent solution. Thanks!!!

  • RobinBeth Faulkner Says:

    When do you have time to make anything? It seems you are always in R&D mode.

  • KathyB Says:

    What firing schedule are you using with these mini-boxes? Also, the pictures look like you are using a top loading kiln — will the boxes work in a front loading kiln as well. Thanks

  • jolanda Says:

    Thank you for posting this Hadar, very useful. If you want to know how deep you are drilling and when to stop, just put some tape on the drill to mark how deep you want the hole to be! Very old trick, very useful though!
    Keep on doing what you’re doing…, jolanda

  • Mona Says:

    Does your brain ever stop? What a great idea

  • Gene Killian Says:

    Yikes! Those bricks are super nasty for the lungs when ground into dust like that. And the grinding process is perfect for throwing that dust up into the air and settling it around the room, from which it is next tracked around into nearby rooms and areas and chuffed up into the air again and again. Do let all know what may be obvious to some, that sawing, grinding, and shaping soft kiln brick MUST be done outside, and with a good dust mask. It is not even suitable to assume that “just a bit” will get around the room and that it could be adequately cleaned up with ease. It will be everywhere in microscopic form, and will forever be taken up into the lungs from that point forward. No exceptions.

  • Loren Gideon Says:

    In your blog you stated that stainless firing boxes contaminate the kiln. Can you expand on that or explain further?

  • Hadar Jacobson Says:

    Melody,

    These boxes go inside the kiln. It’s a kiln within a kiln.

  • Hadar Jacobson Says:

    Christine,

    The carbon cam re-used. No more carbon is burnt this way than with a fiber a fiber blanket box. What I meant is the some kilns burn more carbon than others if you fire overnight. They just keep the heat for a long time after the firing cycle is over.

  • Hadar Jacobson Says:

    Linda,

    It’s worth a try. I tried a big porcelain bisque and it broke. Maybe it was the thermal shock.

  • Hadar Jacobson Says:

    Mary Ann,

    The carbon is only an issue with some kilns, that keep heating after the firing cycle is over. It has nothing to do with what box you use. In general, I fir with no lid, to let the binder and contaminants out. Closing the box may also choke the fire; the carbon meed to be burning.

  • Hadar Jacobson Says:

    Kathy,

    I have been using my regular schedules for quick-fire copper and bronze, which I believe apply to all quick fire clays. And yes, it should work in a front loading kiln.

  • Hadar Jacobson Says:

    Gene,

    Doing it outside is a good idea. But isn’t is better than fiber blanket?

  • Hadar Jacobson Says:

    Loren,

    The stainless steel box oxidizes with every firing ans sheds the steel oxide into the kiln. The black stuff that you see in your kiln after firing is not carbon – it comes from the box, and eventually will penetrate the muffles and the bricks. I have been firing in such a box so many times that it finally disintegrated in my hands.

  • Judy Says:

    Hadar, could the fire brick be sliced and glued together with the glue used to glue it together in a kin? Thank you for always working on progressive solutions and ideas.

    Judy Pagnusat

  • Hadar Jacobson Says:

    Judy,

    I don’t see why not. Whatever is easier.

  • Christine Says:

    Question. I always wait for the kiln to cool down before removing my pieces. Is that necessary, or could they be removed after the firing schedule is complete?

  • Christine Damm Says:

    Thanks for another great innovation, Hadar! Can’t wait to try this.

  • Hadar Jacobson Says:

    Christine,

    No need to wait. Just wear heat protective gloves.

  • Catherine Witherell Says:

    That’s a great idea and very easy to implement. Thank you Hadar!

  • Lynette Fisk Says:

    I made a small box by cutting a 2 1/2″ cube then used a 1 1/2″ paddle drill bit, and turned it by hand. Very little dust created, and it didn’t blow around my studio. I just kept dumping it into a container. Used a serrated knife to cut into the corners. Went very fast….see pics here: http://picasaweb.google.com/bylynette/BabyKilnBoxExperiments?feat=directlink

  • Cindy Pope Says:

    These are very cool. Thanks so much for continuing to come up with new ways to improve firing.

  • DeAnna Says:

    Hadar, Thanks for your helpful information. I love your blog. I have had such a great time working with the white bronze and can’t wait to try some of the other white metals. I have been using silver for over 6 years and bronze since it was released. One question, I made the small boxes. I had the same issue as many with the overheating and under heating of several pieces when using the white bronze and quick fire bronze in one firing so this seems to be a great solution. However, the pieces are now overheating and melting. I also find that even with covering the chambers with fiber paper there is little carbon left in the box (goes from full to about 1/4 full even in the large one) so the piece is becoming exposed. Any solution to over heating and loss of carbon? I have burned up several pieces and keep ordering carbon. I am using the shorter schedule of full ramp to 500 then 400 per hour to 1250. It is overnight in a front loading kiln. Thanks for any helpful hints.

  • Hadar Jacobson Says:

    DeAnna,

    In the small boxes every piece gets more heat, first because of better insulation, second, because it is surrounded by less carbon, and third, because it is not in competition with other pieces. So I would lower the temperature (by trial and error). As for the carbon, I noticed, too, that the carbon burns faster. First thing you can try is to cover the boxes with fiber blanket rather than fiber paper. Another option is to make the boxes deeper by drilling out the inside from the other side of the brick. You can also make them larger so you can fit only 2 of them in the kiln. I am pretty sure that even one large box is a good solution, as long as it lets you use more carbon.

  • Hector Says:

    I now have the mini kiln boxes, a friend has carved them out for me. Will I still need to follow the two phase firing schedule (Pearl Gray Clay)or is there a special firing schedule when using these soft fire brick boxes?

  • Hadar Jacobson Says:

    Hector,

    The firing schedule is the same. You may find that the carbon burns more quickly so fill the boxes as much as you can. You can also cover them loosely with fiber blanket. Good luck!

  • Cheryl Watt Says:

    One other mini-kiln box is made of metal foil that can be fired at high temps and won’t “flake” (and therefore won’t blacken the inside of your kiln) like the stainless steel pans. Here’s a video on how to created one:

    http://www.youtube.com/user/CoolToolsVideos#p/u/0/F-7KO_x7pgw

  • Hadar Jacobson Says:

    Cheryl,

    It looks good although I would absolutely not use a lid. It does not let the binder and contaminants escape, and also chokes the fire which is necessary to reduce the oxygen. I don’t know the properties of this metal, but if you use it do test firing first, since it may require changing the sintering temperature.

  • Chris McCuan Says:

    Did you know that you can buy crucible inserts. I’d say you can get just about this same size or an array of other sizes as well.

  • Hadar Jacobson Says:

    Chris, I was looking for crucibles at the time and could find one that would hold enough carbon. They all seemed too small.

Leave a Reply