Ever wonder how the gold in your jewelry was mixed with other metals to make 14k gold alloy? Didn't know that gold is mixed with other metals? Well check out the series of photos we took recently of Mike making 14k white gold casting grain for a customer's custom ring. The first time I saw Mike make gold alloy, I was amazed that it wasn't more complex. I am not sure why, but I think the mystery of not knowing made me somehow think it needed some industrial size, warehouse furnace to produce molten metal. Oh, how naive I was. Read on...
This is the whole amazing machine sitting on a regular countertop and plugged into regular 110V power. I am not sure whether the height of the unit even breaks a foot and half. The scale at the bottom for those who are curious is a temperature scale. When I took the picture it was well on it's way to the temperature needed to melt gold (1,948°F/1,064°C). The scale reads ~1550°F/~850°C! That of course is inside the enclosure, the metal guard is warm/hot to the touch and well shielded from the crucible.
Mike had the 24k (pure) gold and the master alloy already weighed out. For 14k gold, the percentage by weight must be at least 58.5% of the total weight. The other 41.5% by weight is other metals.
This batch of gold was a standard 14k white gold alloy where the resulting mixture will have about 24% copper, 9% nickel and about 9% zinc. Yes I know that adds up to 42%, but that is just because I was rounding out the exact percentages. The mastor alloy, as it's called, is the whiter metal in the tray and comes premixed from our supplier.
Basically from here we must heat it all up and it mixes together to become alloy gold.
Woohoo, ready to go. The temperature inside the furnace reaches the required temperature and we are ready to go. Yep, that is the machine (doesn't look like much does it?).
Crikey, that crucible is white hot! It really is super bright when Mike opens the furnace.Doesn't take much for the pre-measured gold and master alloy to be dropped into the crucible.
I had to be quick to take the next couple of photos: I didn't want my iphone to melt when I held it over the top of the furnace, and I wanted to get a photo of the metal at the bottom before and after it had melted - it doesn't take long.
Don't be fooled by the red and dull yellow color, it was still white hot like the photo above. The camera just exposed it differently.
It really doesn't take long at this temperautre to turn this small amount of metal into a puddle. I am not sure it was even 30 seconds. Of course the lid gets closed for the time it takes. The photos were taken as Mike opened the furnace up. I snuck a quick look down into the white hot crucible and I had a hard time making out the molten metal from the white glowing crucible. I could just make out the liquid metal sloshing back and forth at the bottom. The photo shows the vague dark spot of the gold, but that is the best my iphone would do getting a shot of it. The molten gold doesn't 'pool' like liquids we think of ie water. It is more like a 'bubble' rolling around on the bottom.
You might wonder how the gold is extracted. Well pretty easy. Mike uses a super tall metal bucket that is filled with cold water. He literally just pours out the molten metal into the water. I managed to capture the water boiling from the heat of the gold just after he had done the pour. I guess someone luckier might have actually caught the gold mid-air but I wasn't. It really just happened too fast.
The yellow at the bottom of the bucket is a ceramic plate that prevents contamination with the metal of the bucket. The gold typically freezes and is solid when it reaches the bottom, so it is there just as a failsafe.
So there it is, 14k white gold alloy. Now you might be wondering why it still looks yellow, well apart from the camera doing funky colors with the picture (Mike's hands are tough and weathered but their not that red and pink!). Gold can never be alloyed at 14k to be the same looking as a white metal such as platinum, silver or palladium. It will always carry some of the yellowness into the final alloy. The mixture was certainly less yellow than my picture shows it though!
So how do white gold rings end up looking the same as platinum? Through rhodium plating. To see how that is done we will have to wait for another post...