Shortening the Firing Time

While experimenting with firing in more efficient ways I discovered something that can shorten the firing time significantly. It seems that the first phase – in which the binder is expended – does not have to be done in a kiln and can be completed in as little as 10 minutes, with no cooling time between phases.

This can be done with the SpeedFire Cone system, on a camping stove, or on the kitchen stove.

Here is how it works:

Pour a 1″ layer of carbon into a small stainless steel bowl. Place your pieces on top of it without covering them in carbon.

Put the bowl on the burner.

Cover the bowl. You can use the cone from the cone system, or the circular fiber box that is actually a firing box, or a fiber board, or a piece of fiber blanket. If you use the cone, cover it with a fiber board or a fiber blanket.

In each of these lids drill a pencil-size hole. To do this in a fiber board or the fiber box you can use a screwdriver. Just twist it in; the fiber is very soft. With the fiber blanket just stick in a pencil to make the hole.

Here are some photos of the set-up:

Fiber board with hole on top

This photo was taken inside my studio, but this should be done outdoors.

Set-up

On the left is the fiber box; on the right is the fiber cone. The pans are flat, but I mostly use simple bowls.

Kitchen

If you do this in the kitchen, the fiber blanket is not recommended. You can protect your stove with aluminum foil.

Turn the flame on to full capacity. After a few minutes you will smell and see the smoke coming out of the holes in the lids. This is the binder burning. I tried to photograph it, but it turns out that smoke and fire are hard to shoot.

After about 10 minutes the smoke will stop. Remove the lid with a glove and peek inside. The pieces should look black.

Before

After

Pour more carbon into the bowl to cover the pieces and put them in the kiln for the second phase of firing. The whole process takes about 2:30 from beginning to end.

I have just fired a batch of thick pieces. If I had done the first phase in the kiln, I would have had to hold for at least 2 hours. Given that the ramping takes about 30 minutes and the cooling time at least on hour, I saved myself 3:30 hours.

Why not burn the binder with a torch?

I have tried this many times. The pieces were positioned the same way, in a bowl with a 1″ layer of carbon. This works only sometimes. In most cases pieces crack from the direct heat, and the cracks do not necessarily show until after the second phase is over.

Why not do the same thing in a kiln?

I have tried this as well. A kiln takes a long time to ramp. This exposes pieces to oxygen for an extended length of time and most probably causes internal oxidation. That means that when they come out of the kiln after the second phase, they may crumble, but not necessarily because they are not sintered: it’s because they are oxidized.

Why is the fiber cone or box necessary?

Without them, it would take a long time for the pieces to heat up and they might oxidize, just as in a kiln. The fiber cone and box create a hotter chamber, partially shielded from oxygen.

A word about internal oxidation: before the advent of base metal clay, I used copper pipes, rods, and wire (solid, or bare, copper, from plumbing supply stores). I used to wrap them with silver clay (low shrinkage) and fire. Cracks would occur because of the shrinkage of the silver, and I had to repair and re-fire. Nothing in the way that the copper looked showed any sign of oxidation. However, after a few repairs, the copper would crumble in my hands.

This is one of the reasons that I avoid firing copper in open air. Even if it looks fine after firing, you never know what is going on inside. Furthermore, sometimes the copper needs to be re-fired, as in repair, enameling, soldering, or adding silver clay. With each firing the copper oxidizes further and weakens, just like what happened with the solid copper.


71 Responses to “Shortening the Firing Time”

  • Georgie Galante Says:

    Did another series today. Definitely need the thicker blanket. I tried to use just the thin blanket and nothing happened, then tried again with both blankets and got smoke and smell. I plan on working off my stove (gas) tomorrow if the weather is nice and I can open the windows…need to watch the parrots, not certain what the fumes might do to them.

  • Jill Averill Says:

    Thanks Hadar for the encouragement and the explanation of the black color. I used both a stainless steel brush and a brass brush (thought I would try both) with soapy water to remove the black. Any suggestions for another way to remove it that will give a different result?

    Now I will do a patina….I am looking forward to see how it turns out.

    I haven’t gotten to my new container of rose bronze yet because I was on vacation, but I plan on using it soon and will let you know how it works out.

    Thank you.

    Jill

  • Hadar Jacobson Says:

    Jill, After firing the piece needs to go through a whole process of finishing using a rotary tool. You can find full instructions in my books: The Handbook of Metal Clay: Textures and Forms, or Mixed Metal Jewelry from Metal Clay. Without sanding, the patina is not going to show the contrast between the different metals.

  • Virginia Says:

    It works, it works, it works!!!
    I made a chamber with fiber blanket around and on top of the stainless bowl and it worked perfectly. Then I tried just the stainless bowl with a fiber board on top and “Wa La”.
    How fantastic to get the first phase done so quickly!!
    Thanks Hadar!!!

  • Linda Reboh Says:

    This is really fantastic, now I can fire everyone’s pieces in class.
    Thanks,
    Linda

  • Christine Damm Says:

    The binder is burned off in this new method, with the pieces in a stainless steel bowl. Then they remain in the bowl and are covered with carbon and moved to the kiln. OK– what about the experiments you posted with the separate small fiber boxes being superior to the large single SS bowl, the advantages being no SS disintegration in the kiln and better sintering because each piece was separate?

  • Hadar Jacobson Says:

    Christine, The fire bricks of which the mini kiln are made are limited in size. Some pieces may not fit in or may not be able to contain enough carbon. It would be nice to have bigger bricks to make bigger boxes. As for the SS bowls, because of their circular shape they distribute the heat pretty well. The flaking is just an inconvenience but I am told that it doesn’t damage the kiln. Truth is, I did make a circular fire-brick box but it fit only pieces of small sizes.

  • Christine Damm Says:

    Thanks for all your help, Hadar!

    If the new method is used, can the pieces (I’m going to be working on less than 2″ size) then be carefully taken out of the SS pan and put into fiber or ceramic boxes into carbon and then covered with more carbon for the second phase firing?

  • Hadar Jacobson Says:

    Christine, If you feel confident about not breaking them I don’t see why not. Since all the binder is gone now, you may find that you need to lower the temp in a fiver box.

  • Dawn Stubitsch Says:

    Do you think you could adapt this method for use with a toaster oven? I have one I use for polymer clay and it goes up to about 500 degrees.

  • Hadar Jacobson Says:

    Dawn, I haven’t tried. Not sure the temperature is high enough. Some binder will burn for sure, but maybe not all of it. Please let us know if you try.

  • Dawn Stubitsch Says:

    Hi Hadar, thanks for getting back to me so quickly. How would you determine that though? I have tried it and it does change color if that’s the criteria.

  • Hadar Jacobson Says:

    Dawn, You should be able to see smoke.

  • Dawn Stubitsch Says:

    I’ll have to monitor it. I didn’t watch. I’ll check it out and let you know.

  • Dawn Stubitsch Says:

    I took two small pieces of bronze clay and put them in a preheated toaster oven at as high as it would go, about 475. It didn’t take too long when the first one started to change color and smoke. I watched for the other to do the same but it took another minute or so and the color change took place but I didn’t see the smoke like I did with the other. I left them in there for about 15 minutes.

  • Hadar Jaobson Says:

    Dawn, That sounds good. Did you fire the pieces to see if they sinter ok?

  • Melody Pierson Says:

    I’m just wondering how I can arrange this on an electric stove? I don’t have fibre board just fibre-blanket…I have the stainless steel bowls…I know the blanket is not recommended for the stove …hmmmmm Any responses would be helpful. Hadar gave the MOST WONDERFUL workshop in near Montreal last week….we all loved every day of it. Thanks, Hadar!!!

  • leigh dunnington-jones Says:

    hello hadar,could i fire a very large piece (13″ tall)in this way? and what would i need

  • Hadar Jacobson Says:

    I haven’t tried, but it may be possible. You will need a big kiln though.

  • connie vickery Says:

    Hi Hadar-

    3 questions:

    – since one can use stainless steel pans on electric stove, can one use a flat bottomed (and dedicated) pan on an electric stove?

    – what were the results people got using a toaster oven or range oven? what temps? use with or without convection?

    – (OT) – could only get Montreal workshop info in french – instruction in english? and where info on where to stay, etc.?

  • Hadar Jacobson Says:

    Connie,

    – It’s best to use the same pan for the stove and the kiln. This way you don’t have to transfer the pieces from one pan to another. They are very brittle at this point.
    – I have not received any reports on using a toaster oven or a range oven.
    – The instruction is in English. Please contact Jocelyne Robertson at .

    Add to Contacts

Leave a Reply