On my Mokume Gane tutorial I have received a few comments and questions in the last few weeks. I am finally getting around to addressing them — sorry folks for the delay! I’ve been a bit overwhelmed with other work.
First off, Athanasios Koumantos blogging at Gaijinto, also has some tutorial information about what he is doing. He mentions using an industrial technique of building a box filled with charcoal particles and then sealing the whole thing using refractory cement to create as oxygen-free an atmosphere as possible. The oxygen sticks to the carbon in the charcoal, or somesuch chemistry like that, and no more can get in past the used up carbon because it is sealed. This seems very clever. Remember that oxidation of any sort is the enemy here.
I have to say that this is a very clever way to go about it. It’s definitely time consuming and uses a lot of resources to do correctly, but I do think it has some merit. If we can’t directly control the atmosphere of the furnace that we use, we can at the very least reduce the amount of oxygen that will get through. Any techniques that are effective are, well… effective. I am interested to see how it comes out.
I used flux in copper-brass and silver-copper bonds without much problem, but the advice I received (either from Reactive Metal Studios or James Binnion, but I can’t remember) was don’t. It can form bubbles or pockets if any gets trapped inside.
To Scott from Slow Rain Creations — you probably want a maximum temperature that is significantly higher than your working temperature so that it can easily modulate itself. If you are bonding at ~1450F for the silver-copper, you probably want something that can go up to 2200 or a bit more.
As for a controller, more precision is better. Especially if you ever decided to try something like the silver-brass, with the eutectic within some small number of the bonding temperature. Try to go for something that can get you +/-5 or 10 degrees. If you’re bouncing up and down around 100 degrees, you’ll probably have a problem at some point. That said, I have successfully done brass-copper in a coal forge with no oxygen reduction — we lost some of the brass out the back because it melted, but the remaining billet was nice and strong. I don’t recommend this adventure with anything more precious than that though.