I was not suggesting anyone try to this, much research is needed, at least understanding the safety factors involved and the dangers, some of which can be unseen (microwave leakage).
Just as with anything we do, we must learn about it and its dangers.
I do suggest studying. And research,
AS of yet this field of microwave technology is in it's early stage of development, and it's use in metallurgy is just beginning to be explored and used, and the possibility's for its use are yet to be realized, some advance's are being made, but much progress will come in the future, with experimentation we will see this used more in the future, and I would not want to stop Thomas Edison from trying to see if he could make that piece of wire glow brightly.
Microwave technology is young and still in infancy, it was not that long ago the man working on a radar tube had a candy bar melt in his pocket, and thought he would put that radar tube in a box and cook dinner, most of us would warn him that is too dangerous.
Fact is for many many years I would not use a microwave to cook anything I ate, I did not want my food (NUKED) cooked (from the inside) with electromagnetic waves bashing water molecules un-naturally I did not trust it to cook any of my food, and I would not have one in my house, and I had some experience with microwave, working with communication towers, they told us the high power frequency's we were working with were cooking us from the inside,
Metals can be melted at 2.45 GHZ. As well as glass. But not without using another material to accept the electromagnetic wave, and induce (current?) into the object being melted (susceptor). Yes sometimes industrially the frequency is different and the chambers are different, but 2.45 GHZ is also used industrially for processing metals in sintering, brazing and other processes, some very much like the home microwave.
Although different frequency works for different materials, this also changes as the temperature changes, here with small amounts of metals
This cannot be done directly, as metals reflect the electromagnetic wave.
Although metal powder will absorb microwave energy directly and begin to heat.
Metals absorption of these waves depend on temperature seems once molecules are moving in the metal they start accepting the electro-magnetic waves easier.
Just as some type of food does not cook well in an electromagnetic wave of 2.45 GHZ, advancement in this field has made progress, and packaging microwave Susceptors (package to cook in, made to accept microwave and convert to heat) example hot pocket package to (bake bread).
I do not think the kits available, or the techniques available as of now are reliable, as the kits rely on (special brand name flux, or material sheets)(me thinks Shore), or relies on material to be melted to contain microwave susceptors, and special boxes containers or refractory shells (refractory again Shor type products), much research needs to be done to find a crucible coating, or flux ingredient (susceptor) which is reliable for this process, and also more study is needed to find a refractory that will allow electromagnetic waves to pass through shell and also contain heat of the melt reflecting the unabsorbed energy back into the melt.
If people who are interested in experimentation give up we will never invent a light bulb, yes electricity is dangerous, and what if Edison and Tesla Quit (because?).
no harm if Edison study's. it is only when he plugs in his lamp will he get fried.
We may have to wait for it but we will see it, a microwave gold melting furnace.