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BRONZclay Fail
I went to the kiln this morning, hoping to “ooh” and “aah” over my BRONZclay pieces that fired last night. Instead, this is what I fished out of the carbon. Eight pieces, all cracked and split open.
I’ve only worked with this material one time before, in a workshop setting about a year ago. My piece didn’t sinter properly and crumbled in my hands. After that experience, I trained my focus on COPPRclay, and of course, the ever-reliable silver clay. I found a firing schedule for COPPRclay that works well for me every time and at any thickness. But, I really wanted to create in bronze and I had 200 grams of BRONZclay on hand. The variety of firing schedules on the web was a bit overwhelming, so I reached out to two metal clay friends who work in this material and asked them what firing schedule they use. Their answers were very similar, so I figured I was on the right track.
Here’s what I did:
- Conditioned the clay according to the info on Margaret Schindel’s BRONZclay Squidoo Lens
- Rolled to 6 cards, then rolled over my texture plate at 4 cards
- Clay was totally dry as it had been in greenware stage for over 24 hours
- Buried in coal carbon in stainless steel firing pan (carbon purchased from WLW and never used before)
- Ramped at 250 per hour to 1516, held for 3.5 hours
- Firing pan pulled out of the kiln when still hot and allowed to cool at room temperature (kiln was not red-hot, but still quite warm – I didn’t note the temperature)
- Kiln is a Paragon SC2
I have a few ideas for what might have gone wrong:
- Maybe I needed to let the pan cool in the kiln, rather than pulling it out
- The lid on my stainless steel firing pan is so warped that it barely connects with the pan. It’s almost like having the pan uncovered. this hasn’t been a problem with firing COPPRclay, in fact I have stopped using the lid altogether for that purpose, but maybe the BRONZclay is more particular about oxygen exposure.
- I used SLIK as a release agent, rather than olive oil
- For the holes that split open, I probably need to leave a wider strip of clay on the skinny side of the donut
I think it’s significant that the pieces appear to be fully sintered. I whacked on them with a hammer, and flattened out some of the domed pieces. They are quite strong and even marred the face of my hammer (darn it). To me, this points to a temperature shock from pulling the pan out of the kiln too fast.
Perhaps someone out there can provide some advice. I’ll also shoot this out to the MC forum for more insight. I really want to create in bronze and I’m looking forward to trying Hadar’s formula and Bill’s new Fast Fire formula, which is coming out later this month. Hopefully, I can figure out how to make something beautiful from the clay I have on hand. I’ll keep trying based on what I learn from this experience.
I am so sorry you had this experience with Bronzclay.
I have a question for you, when you said you conditioned the clay, what did you do to it? I usually take some of the clay out of the package and tried not to stress out the clay as much as I can. I go directly to my working surface and rolled the clay.
In my firing schedule I go up to 1550F and hold there for three hours.
When the firing is over, I do let the pan cool down a little bit before I take it out, usually when the kiln said it is 500 F I take it out and leave it to cool down outside. About your cover, I do not think it plays a big roll in your firing, my cover is very bad too and I fire my work in the pot with it with no problems.
I only use badger to apply in my hands and then I touch my roller and tools.
Keep on trying!! I am sure you will be able to find the right schedule for you.
Thanks, Lorena. I got firing schedules from you and Gail Lannum and they were very similar. I sort of picked at random for my first try and ended up with Gail’s schedule.
The conditioning I did was to work the clay in hand and by rolling – folding – rolling. I got this from the BRONZclay lens and I believe it came from Celie originally.
I think I pulled out the pan too soon. Impatient me!!
I will try again.
How thick do you make your pieces? I know you make complex, layered pieces. What do you use when attaching pieces – water, slip, thick slip, clay?
Thanks!!
I usually make my pieces with 4 cards.
When I add or layer new pieces I use water (when the clay is fresh) and water/clay (when my pieces are dry and they need to me layer or attach to others.)
Hi Wendy,
I feel bad that you didn’t get to “ooh & ahhh” and was more like an “EEEK”. Try not to let it discourage you too much. It does have a learning curve to it.
I too prefer to use the badger balm over olive oil. Haven’t used the SLIK.
I also keep my clay really cold. Have one bowl insde another bowl with ice to keep what I’m not using cold.
If I rehydrate I use a spray bottle that has lavendar oil(few drops) mixed in to help prevent clay from oxidizing.
I let it cool down in kiln(SC2) till just about room temp, will take out vent when it’s down around 500, let cool some more, then open door some if I want to speed it up alittle( probably overly cauious) but works! I try to fire at night so it shuts off about bedtime and is cool in morning just to keep me from rushing it.
The thicker the piece the slower the ramp. I think your ramp was good. I have ramped at 250F p/hr. on some of my thicker layered pieces. 1550F for 3 hrs. hold, but you may find your kiln needs to go to higher or increase your hold time.
Oh, I also make sure I have pan off of bottom of kiln (about 1″) for more even heat.
It does take alittle longer for pieces to dry so make sure it’s really dry internally.
Hope this helps. Wish you luck. Let us know how the next batch goes….
Colleen Wilson ~ Riverview, MI
Hi Wendy,
Thank you for your interest in our clays! Please feel free to contact me with any questions by phone (910-620-8751) or email (william.struve@gmail.com) whenever you have questions.
Neither the fast cooling nor the loose fitting lid are problems. You have full sintering as the material can be hammered witout falling apart. Although it is difficult to tell what size the pieces are, large pieces do tend to develop cracks due to shrinkage. The new FASTfire BRONZclay shrinks less, so this will be less of a problem. All is not lost since you can repair the pieces with fresh clay and re-fire. I now use a slotted lid for all of my work since some oxygen getting into the top of the carbon will generate some carbon dioxide which is needed to scrub the metal particles and promote sintering.
Be well and have fun,
Bill
I’ve found that I have firing failures when I overload the kiln. The very small amount I can fit into the firing box for good results is frustratingly few pieces.
I follow Hadar’s instructions for container-loading and Tony’s firing schedule. I’m now getting consistently good results, as long as I don’t overload.
Lorena, thanks for the further advice.
Colleen, great tips. I’m waiting for the kiln to cool right now, so your timing is perfect!
Bill, thanks for the info and the offer to help. I’m looking forward to a future post titled “BRONZclay Success!”
Elaine, what is Tony’s firing schedule. I’m not familiar.
Hi Wendy,
“Tony” is me. Elaine just left off the A.
Here’s my firing schedule for BC:
BC firing:
1) in kiln on shelf (open air) firing:
a) RA = 250F
b) Temp = 550F
c) hold time = 30 minutes or zero minutes
2) second firing in carbon (carefully pick up pieces and put them in carbon in container)
a) RA 1 = full speed
b) Temp 1 = 1100F
c) Hold 1 = 0
d) RA 2 = 250F
e) Temp 1 = 1490 (1516 with muffle kiln)—adjust temperature for your kiln if you see pimples or pock marks you are firing too hot
f) Hold 2 = 3 hours
Hi Tonya,
Aha! So you are the mysterious “Tony”! Thanks for sending your schedule. I use a 2-stage firing for CopprClay, so this makes perfect sense to me. After the conference I’ll have to give this one a try.
I have some fastfire bronze clay into which I had intended to imbed some cubic zirconia and other high fire stones. However, since purchasing the clay I have been warned that one cannot use these stones in the clay as they will be harmed. Some of the sellers caution not to use stones, but Cool tools says one can sue them. I am puzzled. Can anyone give me help in this matter?