Convergent Series

learning, using & teaching metal clay, and other aspects of life

Smart Bronze: By Jove, I Think I’ve Got It! (Post 1 of 6)

Posted by C Scheftic on 2013/06/28

The newest Hadar’s Metal Clay Powder product is called Smart Bronze. I spent over a month playing around with it, and I think I finally figured out some things about it. (Not everything, mind you, but at last I feel well on my way!) After then spending a few weeks catching up on a several other urgent tasks, I’m hoping I can finally find time to post here a collection of thoughts and experiences.

A Bit of Context.

OK, it’s not like a spent a solid month and more figuring this out. The time I spent did cover most of May, slipping into early June, but it was in dribs and drabs. To begin with, I am not a full-time jewelry artist! I do learn, explore, make, sell, write, and teach about it. Some weeks, it does end up being just about all I do. But there are other stretches when I don’t touch the stuff at all. Most of the time it’s somewhere in between those extremes. Averaging out over a whole year, I figure that I do this about quarter-time, or maybe a third (depending on how you count both “this” stuff and “full” time…), but only that. Whatever the actual proportion, it’s a delightful fraction, I must say! But more than that would feel like work and, though I am trying to treat it all in a very professional way, I also really want to keep this for fun. My point is that the fun I had figuring out Smart Bronze was a very part-time part of that part-time activity: though I’ll drag the description out for several posts, in reality it all went rather quickly.

Also, I have two kilns, in two different styles: one firebrick, and one ceramic muffle. So far, I’ve done all my Smart Bronze testing in the firebrick kiln. When I find some more drib-drab time, I’ll try it out in the muffle kiln too. But if you are reading this in the hope of learning from my experience before firing the stuff yourself, it may help you to know that both my kilns have inside dimensions of about 8 by 8 by 6 inches. The firebrick one can reach 2350°F; the muffle, 2000°F. Smart Bronze fires well below both those limits.

To fire base metal powder clay in my firebrick kiln, I most often use a box I’ve folded myself out of stainless steel tool wrap (e.g., the No Flake Foil sold by CoolTools), and the carbon that Hadar Jacobson recommends in her Instruction Manual (coconut shell-based, acid-washed, size 12×40). With that particular combination of kiln + box + carbon, for the majority of Hadar’s clays, through testing I have found that the ramp-speed she suggests works fine, but I should lower the goal-temperature by about 20°F from what she recommends to get full sintering without blistering or other signs of over-firing. (It could just be a difference in our kilns, but another factor could be that my lightweight foil boxes transmit the heat a little better than the heavier stainless steel bowls I think she uses?) I might do a little more adjusting for smaller containers or much fuller loads, but for what I was firing in these trials, I started out thinking that a drop of 20° should be the only adjustment I’d need.

Finally, whenever I first try any new clay, I always do at least one “test” firing first. I know that some artists plunge right in to make a new masterpiece and just fire it, but I can’t bring myself to risk something like that until I feel really certain I’ve mastered enough of the relevant firing details. At the other extreme, some people will just roll out a plain slab of clay about the same size and thickness as their intended masterpiece, and test-fire that. While much safer, I can’t quite bring myself to simply “waste” a good chunk of metal (even if it’s not a precious metal) that way, not to mention the firing -time and –energy. I have found, instead, a middle ground that works for me: I make several very simple pieces. If they fail, I’ve lost a few more minutes of my time than I would have if I’d just fired a plain slab. But I want to believe that the firing will work and, when it does, then I will have a simple little piece that I can sell inexpensively or give as a small token-style gift (instead of just a piece of “waste” material).

Working with Smart Bronze.

I found the working properties of this product to be comparable to other Hadar’s Metal Clay powders. That is, it is easy to mix into a clay form. It’s easy to work with. It has a very nice feel to it. None of Hadar’s clays are sticky, like some metal clays tend to be. (Yes, you do want to use a bit of olive oil between them and any textures, stamps or cutters you press into moist clay, but it’s not like you have to work in a complete cloud of release agents to keep it from sticking to everything!) Smart Bronze has a very good working time, and it’s easy to rehydrate if you work more slowly. It dries to a very hard state, which makes it easy to clean up and polish pre-fire (which is a feature I really appreciate).

Firing Smart Bronze.

Ah, but now, this is where the real testing comes in.

The latest version of Hadar’s Instruction Manual is always available as a .pdf file for free download from her blog. (It’s available from some other sites too, but Hadar’s blog reliably has the most up-to-date edition.) I first tried firing Smart Bronze when the then-latest version of the manual was from April 30, 2013, and it gave this information for firing that new “Smart Bronze” alloy:

Brick kiln: Ramp at 1400°F/778°C per hour to 1440°F/782°C. Hold 2 hours.
Muffle kiln: Ramp at 1400°/778°C per hour to 1495°F/810°C. Hold 2 hours.

By the time I’d completed my first few test loads, there was a newer version, dated May 15, 2013, and it had been updated to read:

Brick kiln: Ramp at 1400°F/778°C per hour to 1430°F/776°C. Hold 2 hours.
Muffle kiln: Ramp at 1400°F/778°C per hour to 1470°F/799°C. Hold 2 hours.
Pieces thicker then 10 cards or mixed with other metals should be pre-fired.

Notice that, while the ramp (speed) remains the same, there are some significant differences in the goal-temperature from one to the next: a ten-degree drop for brick kilns, and a whole twenty-five degree drop for muffle kilns! So the tests I am about to describe involve changes in temperature that are due to both new temperatures recommendations from Hadar and observation of my own results. (And readers of this blog should be able to skip the first few “issues” I encountered by just checking for the very latest version of the Instruction Manual at Hadar’s website! It’s possible there will be yet more modifications as Hadar travels and gets to see for herself how this product works in many other kilns.)

But this post seems long enough for now. I’ll be back soon with what I found out once I really got going! (Yes, in addition to my earlier comments that my testing spanned more than a month, that’s another really big hint that it took me “several” test firings to work this out!)

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