Convergent Series

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

A Tale of Two Lentils

Posted by C Scheftic on 2013/03/23

One of the early assignments in the accreditation program for Hadar’s Clay teachers involved having to make a sealed, hollow bead, and to fire it. (There’s more than that, but this post is only about that part.)

Of course, who can make just one? I did restrain myself: I made only two. Both are “lentil” beads. One was made from Quick Fire Bronze (which I’ve happily used for ages now), and one using Brilliant Bronze (which is newer to me, and not always successful but one I’ve been determined to master). I made all four “pieces” (both sides, both beads) the same size (diameter and thickness). I did drape the Quick-Fire one over a “steeper” curve than I used for the Brilliant Bronze. After completing the rest of the construction process, I fired them (along with several other pieces I was making for the Western PA Garden Marketplace on April 20). Shown, above, are the results.

The Quick Fire one is shown to the left. It sintered and looks great. It held its curvier-shape well, the seams held, and the kiln gave lovely colors (that, for this exercise, will eventually disappear…).

The Brilliant Bronze one is shown to the right. All the seams held together, no cracks appeared, and it appears to have sintered. Well, to be honest, it appears to be over-fired! It has a rough, sort of pitted, almost bubbled surface. Its edges shrank an extra amount, resulting in a sort of “rim” the whole way around it. Worst of all, perhaps, it slumped a bit: its shape no longer has a nice, even, slight curve to it. Instead, it sort of bulges off to one side (which is hard to see in the photo here).

How did this happen? Well, I knew that Brilliant Bronze should be fired about ten degrees lower than the “other” bronze. But there are several “other” bronzes! And I had a copy of Hadar’s shrinkage-rate chart that led me to believe that it could be fired at either the mid- or high-fire range — and there is a “bronze” that fits the bill for “other” at each of those!

So, here’s the secret: If you EVER have ANY sort of problem using one of Hadar’s clays, first be sure you have the latest information! Always go and check her blog (look at the list on the right side of the screen there). Apparently I had missed that there’d been a typo in an early version of the shrinkage chart, so I had not gone to grab the update. The chart that’s out there now makes it clear that Brilliant Bronze is a mid-fire formula only. Meaning I have to fire it a bit lower than the Quick Fire Bronze.

So the next time I fire Brilliant Bronze, I’ll just lower the firing temperature a few degrees more, and look forward to an even more successful outcome.

In the meantime, though, I have a collection of pieces with butterflies, with roses, and with hibiscus flowers that I made out of Quick-Fire Bronze XT (the high-fire bronze formula) that are calling out to be fired next. Here’s hoping!

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2 Responses to “A Tale of Two Lentils”

  1. Good to know. I’ve fired the brilliant bronze a couple of times with no problem, but not sure what temperature I used. I know my print out of Hadar’s firing directions are old. Will have to check them out.

    • C Scheftic said

      Depending on how long it’s been since you checked this, you may be surprised at the changes!

      There are now two alternatives for pre-firing (aka Phase 1), both of which shorten the total time it takes to complete a load. (Either one takes less time than the old Phase 1, and you don’t have to wait for everything to cool down before you can move on to Phase 2.) The only thing is … be prepared for another round or three of testing in your own kiln before you risk firing anything that took a long time to make! Once you figure out the details for your equipment, subsequent firings should proceed just fine. And relatively quickly.

      Just one caution: because the new pre-fire methods have the pieces simply placed on top of your carbon, not buried in it, there are details still to be worked out about the best ways to approach pieces you would normally position vertically (as I did with these two lentil beads, for which I used the older-longer firing schedule). Ever the experimenter, of course, Hadar continues to explore the best approaches for those. She’ll post the latest information herself, as soon as she figures it out. I’ll report my own subsequent tests here (eventually).

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