For those of you keeping track, this is my fourth test fire with White Bronze. Those first three trials can be seen in last week's post. After contacting the manufacturer, I took their specific notes on my previous firing trials and began by elevating the firing vessel even higher. I increased it's height by adding another set of stilts so that its rim sat just below the top of the kiln. This was recommended since even in my small counter top kiln the difference in temperature from floor to lid can be 300 degrees. My next step was to do both phases of the firing with the pieces buried in the coconut carbon, it was stressed that White Bronze MUST be buried even for the binder burn off phase with the lid off the vessel. Since both phases are being done buried in the carbon in the kiln, there was no need to cool in between, so I took the recommendation of the following schedule:
The above image on the left shows the char on top of the carbon after the completed firing had cooled. This time I definitely smelled more of a "campfire" smell from the kiln than the previous firings, so I do believe it got significantly hotter. On the right you can see the test pieces out of the kiln, they already appeared stronger. There were no cracks and they handled well, so I had hope that the firing had been successful. I took some 220grit sandpaper to the test pieces and removed enough fire scale to reveal a metallic interior. As I had found out last week, the water drop test does not apply to White Bronze and the way to check is to sand with 220 grit to reveal the bronze, without small particles coming off. I was really excited and gave the pieces a wiggle with my fingers, at which point they each snapped in the middle.
So back to the drawing board. What I do know is that the carbon burned hotter this time and the binder appeared to successfully burn out. What I don't know is whether the White Bronze was at its full firing strength. The other thing I learned last week was that even when fired properly, it is very fragile and should really never be used alone. It was recommended that it be used in combination with other materials for strength. If it is used alone and fired successfully, customers need to be warned that it is a very fragile material and does not have the traditional strength expected from metals meaning the introduction of other tools such as hammers or pliers would result in it breaking, as well as if it is dropped on a hard surface. My question still remains as to whether or not I should be able to break it with my fingers. I plan to email these results to the manufacturer to see if this really is the brittle level of this material or if I should slowly bump the second phase firing by 10 degrees. I will keep you posted...