So what wave length would you need for a industrial microwave to melt gold?

You aren’t supposed to put gold in a microwave. You run the risk of bad things.

@filmfann I heard of it done on YouTube, but it doesn’t say the wavelength of microwave to use to melt gold. http://www.youtube.com/watch?v=tB3oQeTG-Mc

I see a microwave kiln kit that is supposed to allow you to microwave gold, but I am suspicious.
I also found this

@filmfann I watched the video… it’s just the impurities that melt… I think you need flux (what ever that means) to keep the gold melting. Also the specific wavelength in an industrial microwave would do better.

Microwaving metal is a bad idea. If you want to melt something metal down just use fire.

I believe that what happens in this process (which seems to use an ordinary kitchen countertop microwave, such as you’d buy in any appliance store) is that the microwaves produced in the heating process are absorbed by the ceramic kiln, and for the most part do not penetrate to the metal ore itself. (Any that do would simply be reflected back to the crucible and kiln, where they would be absorbed eventually to heat the crucible and flux.) That is, the crucible inside the kiln – and perhaps the flux itself – absorb the microwaves and heat the ore that way. The reason it’s not a good idea to put bare metal inside the microwave is that metal doesn’t absorb the microwaves. However, the microwave oven itself is made of metal, and the mesh inside the glass door (assuming you have a glass door) is also metal.

Although I don’t know what material the flux is, in welding flux is used as an oxygen shield to prevent the molten weld metals (the base metal being welded, and the filler metal added to complete the joint) from absorbing oxygen and weakening the joint while in the molten condition. In this process it seems to be an admixture which obviously won’t react with the gold ore but will hold the molten globules in suspension while they sink to the bottom of the mold (and stay molten for the duration of the process) to agglomerate into the desired shape.

But I’m not a metal smelter; I’m just supposing based on things that I know about welding and some things that I’ve been able to google about metal in microwaves in the past ten minutes.

This is a question for LuckyGuy.

There are industrial microwaves designed to do just that. They even melt rocks with them. It would be a BAD idea to try this at home.

Flux, for gold, is borax glass, a (crystalline, slightly alkaline borate of sodium, ..., used as a flux, cleansing agent, antiseptic, etc.) powder that, when melted with the gold, absorbs impurities and allows the gold, silver, lead (that usually occur with gold in white quartz) to form a puddle that is separate from the flux. A refining method used with high heat, as in a smelter.