Sunday, February 5, 2012

Firing pans for base metal clays: how to choose!

Hi bloglandia! I'm Cindy, and I'm a (base) metal clay addict. I have my firing system pretty well worked out these days. It wasn't always like this, though. I remember being very unsure about how to fire bronze and copper. I did a lot of homework, but it much of the information available seemed contradictory. Book learning could only take me so far - I had to test the methods myself!

Since base metal clays need to be fired in activated carbon, you need a container to hold the carbon in. But what kind is best? Many of you probably thought you'd never have to worry about this, since you work in silver. However, now that sterling silver clay is becoming popular, you very well might need a firing vessel!

I can't claim to be an expert, but I can share what I've learned from direct experience using all the popular firing vessels - ceramic, fiberboard, fiber blanket and stainless steel. Here are what I believe are the pros and cons of each. If you've had different experiences, please leave a comment below so we can all learn together!

Ceramic firing vessels
Pros - durable, available in variety of sizes, won't "contaminate" the kiln (more on this later), can be used with a lid or without, transmits heat well.
Cons - susceptible to thermal shock, relatively expensive.

Fiberboard firing vessels
Pros -  won't "contaminate" the kiln (more on this later), can be used with a lid or without, transmits heat well. Thermal shock isn't a concern.
Cons - not as durable, deteriorates after a few firings. Last I checked, was only available in a pretty small size.

Fiber blanket firing vessels
(For this method, you pin a piece of fiber blanket together with steel t-pins to form a firing box.)
Pros - relatively inexpensive, transmits heat well.
Cons - difficult to find materials, requires construction, flimsy, can be difficult to get in/out of kiln, can't withstand the recommended firing schedules for all brands of clay (I had one disintegrate entirely after a single BRONZclay firing - but the pieces sintered just fine at least!)

Stainless steel firing vessels
Pros - durable, cheap, can be used on a camp stove or gas burner to burn out the clay binder.
Cons - relatively poor conductor of heat, might leave kiln dirty.

Here is where the issue of kiln "contamination" comes in. Some stainless steel containers (in my experience, all of the square steel firing boxes - which are actually restaurant food pans, if you want to source them cheaper! - and most stainless steel mixing bowls) will turn black during firing. Black flakes and dust fall off the pan/bowl into the kiln.
My kiln is right next to my Shop-Vac in the basement, so this isn't much of a concern for me. Five seconds of vacuuming and the dust is gone. I put contamination in quotes because the dust is just that - dust. It is easy to clean up and is not ruining your kiln. However it is possible to avoid the dirty part. It seems that there are different grades of steel and some of these don't flake off during firing. Every steel bowl that I have purchased from thrift stores has not flaked, yet every one that I've purchased new has. Go figure.

For the past few months I've used the faster-firing schedule Hadar Jacobson shared on her blog. It really does work with all brands of clay (or at least all the brands I've tried!). This firing schedule is two-phase, with the first phase completed on a gas stove. For this reason, I now only use stainless steel firing boxes and bowls. For awhile I used the lid from my fiberboard box as a lid on the steel bowl, but then I discovered that a aluminum foil pie plate with a few holes punched in it worked just as well (for the gas-stove step only - don't use aluminum in your kiln!). The photo above is my Pocket Rocket stove with a bowl full of metal clay creations hiding under that lid - and my supervisor Indigo in the background.

So there you have it - many options for firing your metal clay creations in carbon! My advice is to keep is simple and use a stainless steel bowl. More money for clay that way! Enjoy your weekend all! ~ Cindy Morris, gogoshebogo design

9 comments:

  1. Hey Cindy!

    Thanks for the post! I use No Flake Firing Foil (available through www.cooltool.us ) It's basically stainless steel foil. It doesn't leave a mess at all, and in my experience, the traditional stainless steel pans start to warp after a few firings with a high temp clay (like copper). The foil is relatively inexpensive and I like being about to create vessels of specific sizes. The one caveat is you have to be careful when cutting/folding them as the edges can be quite sharp.

    A small note on ceramic containers, it seems a few artists have experienced the carbon actually catching on fire and continuing to burn even after the kiln is off. Apparently these containers are porous and more O2 can reach the carbon, while this seems a relatively rare occurrence it's good to keep an eye on your kiln when using it. Since these containers actually hold and conduct heat they can be a really good solution for folks with lots of inconsistent firing issues, so it's a trade off that's worth the risk.

    Thanks again!
    Wanaree

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  2. Thanks Wanaree! I'll have to check out the foil - about how many firings can you get with each container you make?
    And yes, excellent point about the carbon catching fire in ceramic containers. I think this is what happened when I destroyed the fiber-blanket box too.

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  3. Thanks for joining our team Cindy! And thank you for sharing your experiences and opening up a dialogue.

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  4. Thanks so much for the great post, Cindy! Welcome to the MCAM family!

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  5. Cindy, thanks so much for all the information. I also use Hadar's firing method. I have not used the sterling silver yet. Do you use this same 2 step firing method and can you use the same carbon?

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  6. Dawn, I haven't used the new sterling clay yet, but from everything I know about firing, it seems like the 2-stage firing and carbon should be the same. I will let you know if I get a chance to try it!

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  7. HI Cindy,
    Thanks for the posting on this method. I'm glad you mentioned what that was standing in the background too. It looks like a bear.
    I am going to test Hadar's method on the Sterling Silver next week.

    Janet Alexander

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  8. So, I'm in the process of learning how to fire Copprclay and getting it right. Have had one success and two failures. Last night's failure was due, I'm pretty sure, to not enough oxygen to burn out binder. I followed my previous successful formula of firing in lidded container,pieces buried whole time, with lid propped a bit and kiln vented, during slow ramp up and hold at 900, before going up to 1750 for 3.5 hours. So, I'm re-studying. I have a simple question, after reading this AND Wanaree's copper firing guide AND Hadar's updated instruction manual. If you do the binder burnout on the stovetop OR in the kiln, do any of you put a lid on the container for the second phase of firing...the actual sintering phase? It seems to me that no lid is better for binder burnout phase, but a lid would be important for the final sintering phase. Yet, I don't see this mentioned specifically. Thanks so much!

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