Aug 29 2010

“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.


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.


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.


Fill them with ½” carbon.


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.

Aug 26 2010

Little Boxes

I seem to have moved one more step forward on the ongoing path toward better sintering. I was thinking about the analogy of “twins in the womb” and how to extend it to apply it to pieces in the firing box. If twins in the womb steal nutrition from each other, could that be what happens to pieces in the box? If each of them had its own separate space, would they not manage better somehow?

I usually avoid placing a small piece next to a big one, since in my experience, the small ones do not sinter properly. This seems a bit counter-intuitive, since I would expect smaller pieces to sinter better. However, statistically this is the case, and it may be because the heat flows towards the bigger and heavier pieces. So theoretically, if we surround each piece with an insulator such as fiber paper, the heat may not be able to flow from one area in the box to another.

I made a small box from fiber paper for every piece I wanted to fire in a single batch. I filled the kiln with more pieces than I usually do – each in its own little box – and included small, big, and hollow forms of copper and bronze. I used my regular firing schedule for Quick-fire Copper and Bronze, and all sintered beautifully.

Here is how to make the box:

Use fiber paper, ⅛” thick (cheap, and available from glass fusing supply stores). Cut a square.

Cut squares at all 4 corners, each about 2″ square.

Fold the wall upwards and staple.


Make boxes of varying sizes for different-sized pieces.

Fill half of each box with carbon.

Place the pieces in the boxes and fill the boxes to the top with carbon.

Fit as many boxes as you can in the kiln, avoiding the center. (Or could it be that with this method, there is no need to avoid the center of the kiln? I tried it once, and it worked!)

I have fired three times so far in the same boxes, and both the paper and the staples are still intact.

Here is another option: use the fiber board box that I described in my last blog posting.

Cut strips of the same fiber paper, about 2″ wide, and use them as separators.

Aug 13 2010

Please Make Us a Box!

I wish someone would manufacture a fiber box that we could buy and use as a long-lasting firing box for our base metal clay. How hard can it be? Just a step further from the fiber board we use as a kiln shelf.

Until then, here is how you can improvise a fiber firing box.

Buy 2-3 fiber boards. The cost of each is $8-$10.

Use a craft knife to cut a square inside one or two of the boards, about 1/2″ away from the edges. Now you have a fiber “frame.”


The uncut fiber board will serve as the “floor” of the box. Place the frame on top of the “floor.”


As an option, to create a deeper box, two frames (rather than just one) can be placed on top of the “floor,” as shown in the photo below.


Insert nickel-chromium wire (a.k.a. nichrome or high-temp wire) through the frame and through the “floor” board.


Pull the wire through the “floor” and across the outer side of the “floor.” Re-insert the wire through the outer side of the “floor,” and pull it out through the frame.


Cut the wire, leaving at least a 5″ length of wire on each side.

Repeat this with the other two sides of the box.


When making a deep box, instead of a second frame, you can use strips of fiber blanket.


(As an alternative, you can take the small square which you cut out to create the first frame, cut it into strips, and stack the strips on top of the first frame.)

Tie the four ends of the wire together to make a handle for the box.



As a reminder, rather than using a box, you can simply arrange kiln posts around your kiln shelf to make a box.

t-Fiber alternative

(This method is described in the instruction manual for Hadar’s Clay™ Quick-fire Copper and Bronze.) Although this method works fine and is easy to construct, the disadvantage is that it cannot be removed as easily from the kiln, since the kiln posts are not held together.