Testing the Strength of Fired Pieces

How strong should a piece of jewelry be? I guess the answer to this question has changed over the years as new media have appeared in the jewelry-making arena. One thing is sure: we don’t want any piece of jewelry to crumble when a customer tries it on. However, it’s important to remember that jewelry strength is never absolute, regardless of the medium: a piece made of glass can break if it falls on the floor; resin inlay may stick to your fingers in the hot desert; polymer clay jewelry may break with some pressure; paper jewelry may burn if it comes in contact with a lit cigarette.

In other words, there is nothing new about jewelry media that need to be treated with care. Metal clay is one of those media, and in that sense, base metal clay is no different than silver clay. Have you ever tried to test the strength of your silver pieces by breaking them with pliers, or even with your fingers?

Well, after “crash testing” was suggested, I did. I was able to break thin, fully sintered pieces with my fingers. The piece in the photo was made with low-shrinkage silver clay. It is (or was) 2″ x 1½”, constructed out of at least 3 layers, 3 cards thick. Fired in a kiln 2 hours at 1650°F. It easily broke with pliers, after just one bend. And as you can see, the cross section is not so attractive either.

I’ve sold many rings over my metal-clay career. Many of them were returned cracked or broken. I stopped selling metal clay rings, and if a student wants to make a ring for themselves, I tell them to treat it with care.

I don’t see why base metal clay should be different from silver clay in that respect. It is just as porous, and I would expect it to be even weaker because of the firing limitations. I don’t test my pieces with pliers anymore. When they come out of the kiln, I buff them lightly to see if they are fully sintered by looking for any powder underneath. If there is, I re-fire. I don’t try to bend them, either. With silver, copper, and bronze clay, I do all the bending before firing. With metal clay I never make bezels that need to be bent over a stone. I do finish my pieces vigorously. If they survive the finishing process, they are strong enough.

In fact, I started bending and breaking sheet metal to make my pieces, long before I began working with metal clay. One of the reasons I switched from metalsmithing to metal clay is the advantage of being able to do all the bending and joining with clay rather than with metal. Here are a pair of earrings and a ring that I made with sterling silver:

After constructing the ring and the earrings, I bent strips of sterling silver with two pairs of pliers until they cracked. I collected them and rearranged them like a puzzle, and soldered them back on the base structure. I repeated this many times with metal clay, and of course it was a lot easier.

So, sterling silver breaks with pliers. How about brass?

And if you don’t believe the photos, I’ll post a video clip! 🙂

I don’t know where this idea of breaking jewelry with pliers originated, but I am sure that a lot of professional jewelers would shudder at the thought of their creations being “crash tested.” After all, if all jewelry were that sturdy, there would not be a field of expertise called jewelry repair.

I was asked to send my comments on Tim McCreight’s article about bronze clay prior to its publication. Here is what he says on page 6. I did not comment on this because I thought he was right:

“Thicker pieces that have been cut open often reveal a brown powder that is most likely a mixture of copper and tin powder that did not sinter. This hollow core is not itself a problem as long as the outer shell is thick enough to provide the strength required to the piece.”

Well, last night I finished this piece, which is 2″ x 1½”, 5 mm thick. I finished it until my fingers were bleeding. There is no way I am going to crash test this piece!



16 Responses to “Testing the Strength of Fired Pieces”

  • Colleen J. Stella Says:

    HEAR, HEAR!!! I totally agree Hadar! I too would like to know who started this man handling of jewelry…. and WHY.

    Your piece “Inside” is just exquisite!

  • Carol Radley Says:

    Hadar, I agree with you. Taking pliers to a piece of jewelry I’ve worked hard on is not going to happen. Your “inside” piece is beautiful. I think if jewelry is strong enough to stand up to everyday wear it’s fine.

  • Leila Godden Says:

    Hadar, your jewellery is absolutely stunning! The blog is exceptionally helpful and provides an invaluable resource as I begin my exploration of the possibilities with bronze and copper clay. Thank you for sharing so generously and eloquently.

  • Angela Says:

    Thanks for posting this in answer to my question. I myself wouldn’t take pliers to a finished, hard-worked piece either. But to a test sample fired together with it during the testing of a new process still seems to be useful to me. Thanks for your post.
    This is a beautiful piece, as usual.

  • Laura Smith-Hos Says:

    I agree, testing with pliers seems a bit extreme! I do occasionally “test” pieces with my fingers. If I can bend/break them with my fingers, then I figure they wouldn’t stand up to normal wear and tear…but i think MOST jewelry & especially metal clay jewelry can be bent and broken if you apply the pliers! Thanks so much Hadar for sharing all your trials!

  • Tamara Culp Says:

    You expressed my sentiments exactly,Hadar. I expect my jewelry to last as long as it is treated like jewelry, not construction material. Can you imagine what would happen if I took pliers to someone’s 18K gold brooch and then complained that it wasn’t sturdy enough?!

  • Mary Ellin D'Agostino Says:

    Yes, such testing of experimental pieces is one thing, but to do pliers testing on a fully finished piece is rediculous. Especially since the goal of such testing is add pressure until the piece does break.

    People should keep in mind that any metal can have a flaw in it and that the flaw may cause it to break. This is true of cast metals, sheet, wire, and metal clay.

  • Miranda Says:

    HAH, what a silly and wasteful notion this “try to break it up” thing… what for?
    I happen to own an 18K and natural crystal necklace, purchased for fivefigures from a world renowned jeweler. I’ve worn it 3 times maybe and always kept it in its original travel pouch – one of the links in the delicate chain broke. Do I think less of the jeweler? Absolutely not. Would I not purchase again from the? NOT… Do I like my piece less? Nope… Jewelry is portable/tactile art in my view.

  • Sarah Triton Says:

    I completely agree, but actually did break some pieces in my first bronze firing last summer. My largest piece from that bronze batch broke when I tried to use my leather mallet to straighten it out, and THAT broke my heart.

  • ann schneider Says:

    What exquisite pieces and what a genius, both creatively and technically you must be. I love the tutorial on the hinged pendant at the Guild site. It was the first complicated piece I tried and now I understand a lot more than I did! Thank you for all you do.

  • jen Says:

    i love your work! wow ,you are a true artist. i am a beginner at working with clay in comparison. i too sold rings that were returned now i just make for myself… i just starting to use copper and bronze and trying to learn what the heck the charcoal is about. anyway good luck with your book, i just wrote one out in a few weeks and have another out this summer on total different subjects. thanks for this site! xo j

  • Parvez Ahmed Says:

    Hello Hadar
    You have a really impressive article up there. I do not have indepth knowledge about the various metals and its compounds specially it is not my field…I am from a garment manufacturing field. My curiosity led me to your page when I was tryinmg to find a suitable test requirement for long chains. We have designed a garment which will have a decorative chain at the back to hold the garment together. It breaks when I tried twisting it…but it is OK when a person wears it. I was wondering if there is a specific evaluation that could certify the chain as “good quality” by passing a particular pull pressure.
    Could you please help. Thank you.

  • Mimi Says:

    Well, the last pieces I have made either didn’t sinter or broke in two. I noticed that my carbon was taking a long time to cool. Where do you get your carbon and what am I doing wrong? Getting frustrated. I work so hard on a pice only to gave it break in two or have powdery holes in it. Help, hadar. Thank you

  • Hadar Jacobson Says:

    Mimi, I get my carbon from http://www.pmcconnection.com. It is hard to tell why your pieces don’t sinter without knowing what kiln you use, what firing box and what firing instructions you are following. You can write to my email address with all this information (hadarjacobson@gmail.com) or try the Hadar’s Clay Support Forum: https://www.facebook.com/groups/HadarClaySupportForum/.

  • Lisa R Says:

    Hi Hadar,

    Can Steel metal clay be mixed w/ silver clay to add strength? If this is possible what would you suggest for the ratio? Firing time & temp? I was thinking of trying 1 part steel to 4 part silver. Firing at 1650 for 2 hours in carbon. Please let me know your suggestions! I don’t want to waste any materials!!

  • Hadar Jacobson Says:

    Lisa, I have not tried that. What I did is fire silver clay in combination with steel. It made a nice contrast.

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