I've spent the last few weeks exploring White Bronze Metal Clay. The clay comes in powder form and can be mixed easily. The mixed clay is silky and flexible. It was easy to work with and was quick to sand. I was excited to see how the pieces came out once fired, but that's where my trouble began. So far I have fired three different test pieces, each ending with different problems. Below is a page from one of my firing notebooks, and at the bottom are the results. Test Fire #1 was based on the directions from the clay, in the end the center appeared sintered, but the edges were fragile enough to snap off. Base metal clays must be fired buried in carbon, this is done inside a vessel in the kiln. For test firing #2 I altered my firing parameters based on suggestions from my vessel's manufacturer. This time, the piece was far weaker and crumbled like a cookie when wiggled. For my third test fire, I reached out to other metal clay artists working in bronze and adjusted my firing schedule accordingly. This resulted in the piece splitting and then crumbling.
I was reassured by other metal clay artists that initial explorations in bronze required several test fires since everything from the kiln type to carbon type to vessel type to bronze type effects firing, but was still a bit disheartened. I contacted the manufacturer of the white bronze and they immediately responded. You can see in my firing notes below their direct feedback on my trials. The key points include the following:
-The water drop test used in other bronze clays to check for sintering, is not a valid test for White Bronze.
-Both phases of firing must be done in a kiln, buried in carbon - this includes the first phase where the binder is burned off.
-Even the small kiln I use for firing can have a 300 degree difference from the floor to the lid, so the vessel must be up on stilts to best achieve high temperatures.
-The lid should be off the vessel for both phases of the firing.
-When both phases of firing are done in the kiln, there is no need to cool in between.
-The following firing was recommended:
Vessel on Stilts/No Lid for entire firing
Piece buried for entire firing
Phase 1: Full Ramp to 1000F hold 2hrs
Phase 2: Full Ramp to 1250F hold 2hrs
Test cooled pieces with 220grit sandpaper, if it is metallic it's good.
*** On a side note, the instruction manual for White Bronze is part of the manual for the entire collection of base metal clays and therefore a little confusing as they are all talked about together. In the manual, it does say it is a brittle metal when made into thin pieces and recommends it being used in combination with other clays for strength. The email response I receive basically asked why I would be using it alone to begin with and that it NEEDS to be used in combination with other metals. That it should not be used alone and even if you do get it to fire correctly, customers need to understand that their piece will be VERY fragile. This really is different than how it is presented in the manual. I went back and checked on the manufacturer's website and no where does it note that White Bronze is any different than the other base metal clays, you only learn that once you download the manual which I imagine most people do not do until they order it. This is something which I find a bit frustrating, it should be more clearly noted as part of the product description. I really didn't see the red flags until the manufacturer questioned my use of it because the manual is not that direct. My persistence in firing it correctly is partially to see the process through and partially to complete the handful of pieces I have in White Bronze that are waiting to be fired.
So my next step? More test pieces next week based on the above suggestions. Wish me luck!