Breakthrough in Firing Schedules

With the encouragement of the participants in my most recent intensive, and with their kind permission to experiment with their pieces, important progress has been achieved in shortening the firing schedule:

Low Shrinkage Steel XT by itself, as well as Low Shrinkage Steel XT combined with small amounts of copper and Bronze XT do not require pre-firing.

Details:

Two big rings that were fired in a brick kiln for 90 minutes at high-fire schedule (1700°F/926°C) with no pre-firing came out completely sintered. The total weight of the two pieces together was less than 100 grams. They are not shown here because I have not done any finishing on them. An attempt to fire a group of pieces weighing more than a total of 100 grams required re-firing.

The batch in the photo below was fired for 2 hours with no pre-firing. The weight was a little over 100 grams. (It looks like a lot more than 100 grams, but keep in mind that steel clay is very lightweight.) All sintered fully.

Batch

Here are photos of the individual pieces:

Concave

Lentil

Lentil

Hollow

Hollow

Hollow Trapezoid

Hollow

Hollow forms did not crack at the seams, as sometimes happens when they are pre-fired.

Pieces made of copper and Bronze XT, fired at the same temperature, did not sinter. However, small amounts of these clays did sinter when added to steel pieces.

Onlay

Onlay

Twisted

Twisted

Mixed

Overlays

The overlays were rolled 2 cards thick before sanding. All sintered perfectly.

The second experiment was done at mid-fire schedule. After pre-firing, 100 grams of copper, bronze, and Brilliant Bronze were fired for only one hour. All sintered. A batch of 10 big rings only sintered partially. My theory is that the bigger the total amount of metal fired, the more time is required for the heat to reach all of it. What supports this theory is that all repairs, fired for 1 hour with no pre-firing, were successful.

To sum up:

1. Low-Shrinkage Steel XT by itself, as well as Low-Shrinkage Steel XT combined with small amounts of Quick-fire copper and Bronze XT, can be fired for 2 hours at high-fire schedule with no pre-firing.

2. Up to 100 grams in total of Quick-fire copper, bronze and Brilliant Bronze can be fired for 1 hour at mid-fire schedule after pre-firing.

3. Repairs for any of the clays can be done with no pre-firing for 1 hour only.

I am not updating the instruction Manual just yet, since I plan to continue experimenting. Hopefully, more results will be posted soon.


23 Responses to “Breakthrough in Firing Schedules”

  • Cindy Pope Says:

    Wow this is so awesome!!

  • Diane sepanski Says:

    Questions:

    You said in your #1 “sum it up” …Low-Shrinkage Steel XT and Low-Shrinkage Steel XT ……..these are the same, is there a different XT you meant to mention?

    And “to sum it up”…#2…Do you mean 100 grms total work in misc pieces or a 100 gr piece of work?

    Thanks for your continued work!
    Diane

  • Andi Alameda Says:

    This is awesome, I’ll give it a try on some of my low shrink steel this week-end in my Evenheat.

    Thanks for your continuing experimentation!!

    Andi

  • Margaret Says:

    This is awesome!

    My interpretation of Hadar’s post is that we can fire the Low Shrinkage Steel XT alone or combined with Copper and Bronze XT with one firing, not two.

  • Hadar Jacobson Says:

    Diane, I meant to say “Low-Shrinkage Steel XT by itself, as well as Low-Shrinkage Steel XT combined with small amounts of….” 100 grams refers to the total weight of pieces in the firing. I’ve now updated the text of the posting to make this clearer. Sorry about the confusion!

  • Sharon Says:

    Hi Diane,

    In Sum #1 it reads Low-Shrinkage Steel XT and Low-Shrinkage Steel XT combined with small amounts of Quick fire copper and Bronze XT—-meaning the second reference to Low-Shrinkage Steel XT is in combination with Quick fire copper or Bronze XT.

  • Marie Green Says:

    Hello Hadar,
    This is wonderful news!! I can’t wait to try it out. fyi…I just sold the steel tower ring we made in last year’s architectural class…thanks to you!!

    Thanks again for continuing to make improvements to the process and keeping us all well informed.
    Have a great day,
    Marie

  • Jocelyne Roberson Says:

    This is fantastic, I should try some to. I’ll let you know

  • melissa richardson Says:

    oh, hope this works for me. having so many problems with steel

  • Lorien Says:

    I am so excited to see the post!!! and the summary is so helpful!

  • Kelly Says:

    Great!!!!! I will try this weekend!!! Thanks Hadar!

  • Liz Says:

    This is great news! Has any such experimentation been done with white bronze? The difference in my WB firing temperatures is small – 1100F for phase 1 and 1323F for phase 2. Perhaps I’ll give this a try and report back, unless you have any specific info as to why this is not recommended?
    Thanks! Liz

  • Michele Milana Says:

    Thank you for your continual research. I am transitioning to using only your clays because of your dedication to making sure the quality is the best and that the directions are clear and up to date. Great work. And I love your pieces!

  • Marlynda Says:

    This is great news, Hadar. Pre-firing using copper, bronze, and brilliant bronze for the few minutes required and being to do the second firing in 1 hour really makes teaching a base metal clay class so much more doable. It makes a one day class realistic.
    Yea!

  • Hadar Jacobson Says:

    Liz, Haven’t tried yet. Please report to us.

  • Hadar Jacobson Says:

    Marlynda, Just make sure you don’t exceed 100 grams. A kiln full of students’ work may not be able to do this in 1 hour.

  • Donna Says:

    Were they fired on a shelf or in carbon?

  • Hadar Jacobson Says:

    Donna, if you mean the steel pieces, they were fired inside carbon. The copper/bronze pieces were pre-fired on top of carbon, them covered with carbon for phase 2.

  • Liz Says:

    Re: White Bronze short fire.
    Hi Hadar,
    I experimented with firing 6 pieces of WB (total well under 100gr). 3 were small, raw pieces and the other 3 were larger pieces in for repair. I fired to 1323F for 1 hour.
    Result: the raw pieces sintered fine, but the repaired pieces not at all. Curious.
    I will refire the repairs for 2 hours.
    Any ideas on why this happened?

    Liz

  • Hadar Jacobson Says:

    Liz, Re-firing White Bronze (only White Bronze) doesn’t help it sinter if it didn’t sinter the first time. It will sinter only if you add fresh clay in the spot that did not sinter.

  • Pamela Pollock Says:

    hello hadar, i just did my first firing according to this revised schedule. i combined steel with bronze and steel with some clear cz’s. the thicker pieces in the firings appear to have sintered at 1700 F for two hours….however a very thin ring that i fired in that batch (all steel) didn’t sinter and broke when i attempted to break it on purpose with my fingers. also, i don’t have a hole in the top of my kiln….just the port hole that you can block on the side. do you think that would affect the firings? thank you for all that you do to speed things up for us!

    pamela

  • Pamela Pollock Says:

    oh and one hollow rock piece that had 4 card thick walls didn’t sinter all the way either.

  • Cindy Pope Says:

    I also don’t have a vent hole and wonder if I should add one now to my brick kiln.

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