Thanks for that link, Arrow! Great idea. I've been wondering what to do with the old microwave I've got sitting out in my garage unused. Now I know.
Well, I know from my research that metal clay or silver clay, as it's sometimes called, is 99.9% fine silver after firing and the gold is 24K, so, yes, they are very pure. You're right that the means to atomize bronze is beyond the capability of the average person, but that's not necessary, anyway, as atomized bronze powder is readily available. The issue of the metal content is moot, as well, since, once the wax burns out and the bronze is sintered together, you've got pure bronze that is exactly the same bronze as before, only fused. The process of firing it won't change its fundamental composition, just its state. It goes from a powder to a solid.
I'm not sure you're right about that high pressure part, either. I know that rapid metal printing can produce bronze parts (and other metals, as well, including steel) without any pressure applied at any point in the process. Also, in rapid metal printing, there is no furnace used. The metal is laser sintered. But, that's probably a different process than the one you had in mind. It does use atomized metal, though.
I'm really intrigued and excited about the prospect of using a microwave for this. I hadn't even considered it as a possibility. The 1000 C temp quoted in the article (1830 F) is perfect for use with metal clay, which needs to be fired at 1650 F (for PMC+) for 10 minutes, or 1830 F for two hours for the Gold PMC. Since silicon bronze melts at 1780 F, this would be perfect for bronze, as well. Good thing I have a spare microwave, as I'd hate to have any burnt out wax residue all over the inside of the one I cook my meals in.
P.S.: well after reading the article, I'm a little disappointed to learn that the temps attained were the result of using an investment casting mold material that contains graphite and molochite. Obtaining either shouldn't be expensive or difficult, but I was hoping to be able to use the microwave for metal clay, as well as for trying my bronze clay idea. Maybe if I made a box with a ceramic/graphite/molochite shell into which I could place the metal clay object...but, then I wouldn't be able to keep an eye on it. Hmmm....