Convergent Series

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

Posts Tagged ‘shrinkage’

Well, that was a surprise!

Posted by C Scheftic on 2016/06/30

As promised in my last post, here’s the story behind the earrings whose photo I posted there….

1. In my fairly early days working with metal clays—as soon as I’d moved on from just using a creme brulee torch and bought my first kiln but when I was still working on tray-tables in my family room, years before I started this blog or opened my studio—I found much inspiration in the work of CeCe Wire (one of the pioneers in metal clay techniques), and one of the things I had fun doing was making pieces that played with shrinkage. I learned about the concept in her first book, from 2003, Creative Metal Clay Jewelry: techniques, projects, inspiration, and had that reinforced when I earned my PMC Certification in a course with her, in Baltimore in 2007.

At that point, I’d make a small piece (earrings or small pendants) out of the original PMC Silver formula (no longer available), that had a shrinkage rate of 28% (and had to be fired in a kiln for a full two hours). I’d embellish it with Art Clay Silver, that had a shrinkage rate of 10%. Why those two? Because their shrinkage rates were the farthest apart of all the clays at that time on the market.

Because it was constrained by the low-shrinkage clay, the high-shrinkage clay would curve and distort in interesting ways: the fun part was trying different locations for connecting the clays to discover what results I could produce. (This was also back in the day when the nominal price of silver was a mere fraction of what it is today…. I am so glad I started that early! Even then, I did feel limited in how much sheer experimenting I could do, but nothing like it would be today….) I did some other clay combos too, but that particular pairing consistently yielded the most interesting results. The relatively high shrinkage of “original” was the key, no matter what other clay was combined with it.

I stopped doing any of that when Mitsubishi discontinued their original formula. Like many others, I was sad to see it go, but I created enough designs in other ways that the loss didn’t feel as devastating to me as it did to some folks. Since then, a few other silver clays have come on the market with shrinkage rates in the range of 20 to 25%, and at times I’d think about reviving that old technique with them, but then would get caught up in other project ideas and that would slide way down on the priority list.

2. I have written here before about how I try to not store “leftover” clay. I just keep making things until I’ve used a packet all up. Some of my earrings are made with leftover bits. Little embellishments can be cut out or coiled up, dried, and used in later creations. The last few dregs can be shaped into little balls, dried, and stored for later use too. If I don’t have time at the end of a work session to use everything up, I will store the last bits for a brief time, but I do try to form those into something useful as soon as I can.

3. Last month, for various reasons (e.g., different projects, classes, demonstrations), I used a number of different clays, including these (as well as several others, but these are the ones relevant to the rest of this post):

Clay Formula Shrinkage Rate
PMC 3 12%
PMC Flex 15%
PMC Sterling 15% – 20%
.960 made with PMC3 Question #1
.960 made with PMC Flex Question #2, this post’s inspiration…

Re Question #1: In a comment on the post where Celie Fago introduced the idea of home-made .960, Holly Gage estimated the shrinkage of PMC3 and Sterling to be about 13%. In a post that further disseminates the idea of using .960, Emma Gordon writes that “You can use PMC3 syringe with it, no problem.”

Now, maybe I’m missing something obvious, but if folks are combining PMC 3 syringe clay with .960 made from mixing PMC3 and PMC Sterling, it seemed as though I should be able to combine PMC Flex lump clay with .960 made from it and sterling: their nominal shrinkage rates are even closer! I had a bit of Flex.960 left from one activity, so I used up those dregs making a couple little pairs of earring bases. Flat ones. Definitely flat. I had a bit of regular Flex left, so I twisted a little spiral-pair for one set of earrings, and made a little twisted rope to embellish the other pair. (With the last few bits, I made a number of little balls which I then accidentally knocked all over my studio floor. I’ll hunt for those eventually!)

And when I fired those two pairs of earrings … the photo below shows what I got! Can you see how far they’ve curved?!! I’m not disappointed in the results. In fact, I’m happily reminded of those early CeCe-inspired domed pieces that were so much fun. It’s just that this is not what I was expecting! The shrinkage rates on these clays are nowhere near as far apart as what I was using in all domed pieces I was making a decade ago — I would have expected this with those. Just not now.

I guess this is telling me I need to find some time (where?!!) to do some more experiments! If you’ve experienced anything like this, intentionally or not, please let me know.

Posted in General Techniques, Misc. Musings | Tagged: , , , | Leave a Comment »

One Thing Just Leads to Another

Posted by C Scheftic on 2014/02/01

If you’ve stumbled across this blog / post without a lot of previous metal clay experience, you may want to just click on the photos to enlarge them and read the brief notes there. For the rest of you, I’ll start by asking if you remember the earrings I wrote about last week?

For today’s post, I’ll start by saying a little about the steps I went through in making the bronze-parts of the two-metal earring pair I described earlier.

  • Grab a good-size chunk of Champagne Bronze clay.
  • Roll it out to a thickness of four cards.
  • Position cards around it, two cards high.
  • Use a thin, straight edge to cut two distinct sets of five intersecting lines. (This was done freehand, so their positions are similar but not identical.)
  • Use a circle cutter to make two “large” circles.
  • Use another circle cutter to make a “small” circle inside each of the “large” ones. (Again, done freehand, so their positions are similar but intentionally not identical.)
  • Do all the usual clean-up and drying of the various bits of clay.

When the circles had dried, I used the small, matching “inner” circles (where each set of lines all intersect) over some Low Shrinkage Steel XT to make the earrings I mentioned before. So far, so good.

Looking at the dry “outer” circles (washers, actually: the larger circles with their centers removed), I had another idea. Using a texture sheet with some concentric circles, I rolled out two more sheets of clay, one each from Friendly Copper and Low Shrinkage Steel XT. Then I centered one of the bronze “washers” over each of those, and cut a matching circle out of each clay. Finally, I rolled out another pair of those two clays, this time using two different “flowered” textures, and cut out a third circle of the same size from each of those. Both the circles- and the flower-design were rolled to four cards at first and then, with the textures, down to two cards. (I didn’t roll the clay with textures on both sides because: (a) I hadn’t yet decided for sure how I would use them, and (b) I wanted to center the designs on both sides the way I wanted, and doing that separately for each side was easier.) I set all those aside to dry (as well as a few other bits I’ll try to write about another time), figuring I’d use them for something….

A few days later still, I got to wondering about the “high fire” temperature of these new “one fire” clays. In general, even with this new trio, it’s the bronze that’s going to limit how hot the product can get during the sintering process. Would the “bronze embeddable” bails survive that heat? (I use them myself, on occasion, and I often offer them to students, especially in introductory workshops, because they can save a bit of time when compared to having to make one’s own bail.) So I took one of the bronze washers, attached the copper disk with circles and let that dry, then positioned the embeddable bail and attached the copper flower-design disk. Once all that had dried, I filled in a few little gaps, dried it all some more, and finally fired the piece.

The results were interesting, as shown in the first photo, above. It all sintered just fine. The bail did blister a little bit: not enough to ruin it, but enough that any metal artist “in the know” should be able to spot what happened. But I still think it’s interesting.

There was one small blister on the sintered bronze section. My first thought was that I’d overfired the batch a bit, but then I realized it was exactly over the post on the embeddable bail. Silly me, I didn’t think to capture a photo of that: What I did was to immediately see if I could polish it out. Easy! I’m not done polishing this piece (it was just a spur of the moment creation, not a planned project), but I think the photo I include here (click on it for a bigger version) gives you a hint as to the blistering on the bail (in case you’re someone who uses them too), and to the way it does look like the disk itself will polish up nicely with a little more work.

There’s one other item worth noting: how the bronze in the bail alloyed a bit with the copper on the other side! Look at the side shown to the right in the first photo, up near the bail, and notice the golden-colored patch. Alloying! Again, artistically, I’m OK with its looking like that. But it’s good to know it will happen.

A few days later, I got to wondering, would the bronze wire I sometimes use with such pieces show the same blistering? [Later clarification: I’ve used that wire in the past with pieces made using Hadar’s Quick Fire bronze. That’s a clay that takes a two-phase firing and only mid-fire temperatures and it’s always held up beautifully in pieces fired that way. Here, I’m otherwise reporting on the newer one-phase high-fire clays.]

So I made a simple wire-loop bail out of phosphor bronze (melting temp listed as 1800°F), then took the other (matching) bronze washer and the Low Shrinkage Steel XT disks, and assembled it the same way as I’d done before. I fired that using the same schedule too.

And, again, I noticed a bit of blistering on the bail and, with this wire-design, a bit of fusing across the loops. Again, I think that slightly grainy look is OK. Other than a quick clean-up, I have not yet stopped to polish this one at all. But I decided to post about it quickly because, this time, the main piece shrank much further away from the bail. In its clay state, the loops were pressed lightly down into the piece, but the post-firing separation is visible in the photo. No alloying with the steel though, which is also good to know.

But you have to see the two together to catch what surprised me the most: the difference in shrinkage! They started out exactly the same size, and look how different they are now. The current (as I write this) Hadar’s Cheat Sheet (.pdf) says that, on their own, Champagne Bronze shrinks about 30%, Low Shrinkage Steel XT about 28%, and Friendly Copper about 25%. Combos will be limited, to some extent, by the least-shinkage clay in the mix. But there’s only a 3% difference between LSStXT and FrCu, and it sure looks to me like there’s more than a 3% difference in the results here. What I can feel, but can’t really show here, is that there is maybe a 3% difference in height but it’s in the wrong direction. The one made from copper is a teensy bit thinner (i.e., more shrinkage, not less).

I really do like the results I’m getting with these clays, and the 3-hour firing time is a huge help compared to some of the others. But, with the others (and any of the “older” clays, both precious and non-precious), I think I have a pretty good feel for the shrinkage. With this new One Fire Trio, I’m still exploring….

What are you finding with them? Do leave a comment!

Posted in General Techniques, Learning Metal Clay | Tagged: , , , , , , , , | Leave a Comment »

Pushing, in more ways than one….

Posted by C Scheftic on 2012/07/18

About a month ago, I wrote a post about some pieces I am calling “Push Pendants” because they are made by pushing some metal clay through a piece of metal mesh. Given that I like making reversible pieces, furthermore, if you read my last post you would have seen a photo of the “other side” of yet another one of these pushed-pieces. The first photo with this post shows its pushed-side, all polished up to a nice shine. (You should be able to tell from the shape which (un-polished) “other” side it matches there….)

They’re fun to make, and I admit the original idea was not mine. They are adapted from a slightly different project I noticed a while ago in Mary Hettmansperger’s delightful book, Mixed Metal Jewelry Workshop. The approach used by “Mary Hetts” is really simple: you make the combo, fire it, then frame it in sheet metal. (Check out her book for all sorts of other useful details!) That strategy minimized one major potential issue: as the clay is fired–both burning off binder and sintering the powder into a solid metal–it shrinks. The wire mesh does not shrink. Warping and cracking can occur in the parts that began as clay! Her process minimizes that as a problem by having you frame the sintered metal with some other solid product (e.g., sheet metal, but you could use wood or fiber or plastic or whatever else you want). First of all, you don’t get very much cracking that way; secondly, you can probably just cover up any you do get.

But I started to wonder: what if you just framed it with more clay from the start? How much of a problem could that be? What are the variables involved? How much more difficult would that make the whole task? Would it still be a good project for a workshop that included both experienced and novice metal clay artisans?

After several months of experimenting (and confirming a few of my suspicions with Hadar Jacobson at the recent PMC Guild conference), it is looking to me as though:

  • With these, it helps if you are someone who is willing to accept what the kiln gives you: they’re not totally unpredictable, but even tiny variations in construction can have very noticeable effects!
  • Giving the piece a bit of curvature, a hint of the direction in which you want it to warp, can be helpful.
  • Really thin surfaces, front or back, do tend to crack.
  • Thicker surfaces have a more complex relationship to the warping and cracking, but there are ways to minimize such problems (and to make it easier on yourself to patch cracks and refire if you find that desirable).
  • The position of the mesh in relation to the frame matters as to whether and how much the piece will crack along the side.
  • The variance in shrinkage rates across the different clays makes a difference in the patterns of shrinkage and warping in these pieces. The pattern of least to worst is predictable; the exact extent seems not to be.

I’ve had people ask me why I bother with these clays if I have such problems with them. Well, the answer is that both the explorations and the results are, overall, delightful. Most of the time, pieces do turn out fine. And some of the so-called problems that do occur are ones I’d never have with silver because it’s just much simpler and more reliable to fire. But I realize that others happen because I try things with these metals that I would never think to try with silver or, if I did think of them, would be unlikely to try because of the price of silver.

In this example, besides simply pushing clay through mesh, I feel like I am pushing the envelope; that is, I feel like I am also extending the current limits of the clay’s performance, going beyond some commonly-perceived boundaries of working with it. I find the process of exploration to be fun, itself, in addition to any reactions I have to the resulting pieces or the subsequent workshops I may teach from what I’ve learned.

Posted in General Techniques, Learning Metal Clay, Teaching Metal Clay, Technical Details | Tagged: , , , | Leave a Comment »

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