More Bonzclay

I've been working with Bronzclay now since Thanksgiving.  The last pieces are going into the kiln today.  And if none of them have to be refired, I'll be finished with bronze for awhile.

The clay is so nice to work with that I ambitiously made a couple of larger pieces before I realized that bigger, thicker pieces need a different firing schedule. I found some iris pods in the backyard last fall and thought they would make a nice focal piece for a necklace. But the piece I lovingly created turned out to be 13mm thick in the center.

While there is a lot of information about firing this clay out there on the Web,  I decided to contact the manufacturer himself for advice.  Bill Struve was very helpful and patient with all my questions as we exchanged a few emails.

We decided that the slow ramp process Mardel Rein has devised, which takes into consideration the type of kiln, the thickness of the clay, and the target temperature, would be appropriate to try.  So after an initial open air firing phase, ramping at 500° to 650° and holding for 45 minutes, I covered it with carbon and fired at 115° per hour to a target of 1490° and held for 3 hours.  Yes, the piece was in the kiln all day.

One of the pods broke at the seams but otherwise the piece was intact.  It was an easy fix.  The second firing used the same first phase.  But then buried in carbon it was a full ramp to 1510° with another 3 hour hold.  Bill Struve had told me that the slow ramp on already fired items wasn't necessary.

Cleaned up and polished, this was the result.

So what did I learn?
While bronze clay is so much less expensive to purchase than fine silver and I feel compelled to create larger pieces, firing time can cancel out the savings, even when you have solar panels.  So it's not something I will do often.

I'm thinking about digging out my husband's dehydrator.  Some of my smaller/thinner pieces tended to crack or break but they always seemed to be pieces with more than 1 layer and cracks began in the layered area.  It's possible that even pieces that sit around for awhile are not fully dry in the center of the thickest part.  Pieces that sat for a week fired without problems.  Those that were only a couple days old were the ones that cracked.

The shrinkage rate of Bronzclay makes it difficult to create my openwork/filigree designs.  Even when my coils are thicker, they don't seem to stay together.  So I may go back to Goldie Bronze for those designs despite its more grainy finish.

As I stated in an earlier post, bezels need to be attached to already fired pieces and the entire work fired.
 again.  Second firings can be at full ramp to target temperature.

Any pieces with nooks and crannies should be fired in a wire mesh cage.  Because of the shrinkage rate of Bronzclay, this is particularly important.  Small bits of coconut carbon can cause cracks in the design or become embedded in it.

My kiln is a Paragon Firefly and the bonding agent in this clay just would not burn out using the manufacturer instructions.  I had better results using a first phase firing on a kiln shelf then burying the pieces for the second phase.  I do this with both thin and thicker pieces.

A New Year with a New Bronze

Happy New Year!!!

I've been away from my blog but not sitting idle. In my last post I talked about my firing issues with Bronzclay.  Since finding a firing schedule that works I've been hard at work testing the clay with my new designs.

I'd like to report that some things work and some don't.

These small pendants were quick and easy and fired nicely.  Only the pendant on the far left had to be fired a second time.  I found when layering or attaching elements water is not enough to keep them together in the kiln.  Most attachments need a loose mixture of clay and water covering the entire surface of the adhesion.  If there are any spaces the piece will begin to separate.

I like to add flowers and curly snakes to some of my pieces.  But sometimes the little particles of carbon that the bronze is immersed in get stuck in all the spaces my style provides.  Sometimes that just means digging these particles out  but occasionally they interfere with the shrinkage.  This bronze clay shrinks a lot, about 20%, so the carbon particles immersed in a design will cause it to crack.  To solve that problem I've purchased some stainless steel wire mesh to cover the delicate pieces and keep the carbon particles out.

This high rate of shrinkage also makes it impossible to embed a bezel setting for even a small stone.   Because the setting doesn't shrink it causes clay around it to crack.  Bezels need to be attached to fired clay and the whole piece fired a second time.

It's been a learning process but all in all I'm happy with the finished products that have survived the kiln.  My new inventory for 2014 has some new designs I hope people will like.  Bronzclay is a joy to work with and the finished product sands to a lovely shine that I protect with clear coat.

Here's a sneak peak at more of my new jewelry soon available at Jansjems--

Adventures in Bronzclay

I've been working on a custom order for the past week.  The order is for a bronze pendant which came out beautifully and only took 1 day to create.  But I've spent the last 5 days trying to find the proper firing schedule for it.

I made a real rookie error with this order--I created the piece from a product I've never used before.  I've tried and successfully created jewelry from a couple of different bronze clay products.  These were powders that you have to add water to.  Their firing schedules are pretty easy and one is even comparatively short. But I didn't like the final color of one and the other shrank way too much.  But an instructor suggested I try Bronzclay.  It comes already in clay form.  As I was almost out of bronze clay, I ordered 200 grams.

My friend was right.  It's not grainy like one of the powdered products, stays moist longer, and reconstitutes easily.  So right out of the package, after working it a little, I created my custom order.

I also created a couple of test strips and fired them together according to instructions in the package.  The thinner (2mm) strip came out fully sintered but with pinholes.  I'm no expert but I think that means it was over-fired.  The thicker textured strip (3mm) snapped in half when I tried to bend it and the black bonding material was exposed.  What does it mean when the binder burns off on 1 piece but not the other?

I adjusted the schedule a bit and tried again to fire a pair of earrings.  This time the binder didn't burn out on either piece.

What did we do before we had Google and all the information people throw up on the Web?  In my search for sintering problems and firing schedules for Bronzclay I found that I was not alone with my problem. There were no less than 6 different firing schedules put up by metal clay experts that work for them.  Some used a single firing method buried in carbon, some used a 2 step process in carbon, some fired initially on an open shelf then used a 2 step buried-in-carbon schedule.  Others followed the open shelf with a 1 step schedule.  Some schedules were for specific style kilns.  All are very long schedules--easily 9 hours.

After 4 days of trials, the open shelf initial firing to burn out the binder did the trick but the follow up firing caused my next pair of earrings to become brittle and break.  But using a 2-step ramp up and dropping the final temperature some in the second firing seemed to do the trick, at least for the small flower pendant I made.

How you dry the clay may contribute to the problem. It shouldn't be put on a coffee warmer but instead needs to air dry. I found articles suggesting freezing the clay to dry it.

I'm not sure that makes any difference but before I put my custom pendant into the kiln I decided to try a few more pieces to see if I get the same result.  These were also left in the freezer for awhile before firing though I'm not sure why I did that.  They had air dried for a couple days already.

After the successful firing of a few more pieces....

I fired the custom piece.   Voila!!

This bronze product polishes up nicely too.

For those who might be interested, and to add yet another firing schedule to the internet, I achieved this success by placing pieces on an open shelf and a slow ramp of 250°F to 560° F , hold 30 min and cool down.  Then burying pieces in coconut carbon, full ramp to 800°F or 900° F, no hold and ramping at 250°
to 1468°F, hold for 2 hours and cool.  Yes, it's a full day in the kiln.