Convergent Series

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

Smart Bronze: By Jove, I Think I’ve Got It! (Post 2 of 6)

Posted by C Scheftic on 2013/06/28

This post continues the story I started this morning, reporting activities from last month….

Trial #1: Early May in Brick Kiln

Hadar (back at that time) said: Ramp at 1400 to goal-temp of 1440 and hold for 2 hours.
I entered: Ramp at 1400 to goal-temp of 1420 and hold for 2 hours.
This should have taken just over 3 hours; the program completed in 2:42.

Test pieces: one small stamped disk and one “golden threads” loop (the latter was a simple project from Hadar’s blog when she introduced the product she calls Brilliant Bronze).

Results: Two test pieces were simultaneously under- and over-fired! That is they were under-fired in relation to the debindering phase, and over-fired in relation to the sintering phase.

How did I know this? What I found were small, uneven blobs of bronze (i.e., over-fired at the end) that, when handled and examined, disintegrated into small bits of metal and dust (i.e., under-fired at first). The firing finished late at night and I was tired and a bit frustrated: I tossed them before thinking to try to take a photograph.

What to try next: Even though this material can be fired in just one round, the conditions still have to be right for both (1) debindering and (2) sintering to happen as desired during the (1) ramp and (2) hold phases, respectively. Clearly, this kiln-program was not the right one on either count. I’d have to adjust it in several ways.

Trial #2: Early May in Brick Kiln

Hadar (still, back then, though later revised) said: Ramp at 1400 to 1440 and hold for 2 hours.
I entered: Ramp at 1375 to 1410 and hold for 2 hours.
This should have taken over 3 hours; the program completed in 2:45.

Rationale for my new program: (1) I was hoping the slower ramp would allow for better binder burnoff. (2) Since Hadar’s other clays all worked great for me at 20° less than her posted temperature, I wasn’t yet ready to go plunging further than 30° below her number.

Test pieces: two more “golden threads” loops that I’d made along with the first-trial one. (Thinking I’d done with testing after one try, I’d added small ball embellishments to these.)

Results (shown): Both test pieces seemed, at first, to be a bit better debindered and sintered than the previous trial. They did show some signs of melting, but nothing like the last time. Still, they broke under very light pressure while holding them to photograph them. It was hard to see the inside of the small ends. They might have been somewhat sintered, but certainly not fully so. Still, this felt like some (if small) progress from the first mess.

At that point, I took some time off from this testing, and will pause my report here. Before I close this post, however, I’ll add one other thought.

A Comment on the Name: Smart Bronze.

As a customer, who is buying this product to use myself, the name almost makes some sense. First of all, unlike many other base-metal clay products (from Hadar and others), it should be possible to process this one in a single (reduced oxygen) firing. Many of the others require two firings of one sort or another, but this product was developed to be “smart” enough to both debinder and sinter all in one go. Which is very convenient! Also, it does polish up to a lovely color, a color that one might call “very smart”…. (And, for anyone familiar with Hadar’s Clays, a curious pun in comparison to her Brilliant Bronze.) But, as a maker, I do find it an awkward name. It’s not one I would want to use on the label of a piece I made using it. More on this in a later post (most likely after I’ve finished this whole series on testing).

Because that’s it for right now. But I’ll be back as soon as I can with more info.

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