Help with alloying gold

Jewelry Discussion
1

Can someone please help me… I’m baking my noodle! :exploding_head:

I have 3g of customers own 9ct gold and I need to bring it up to 18ct.

If my 3g of 9ct is 37.5% gold then it contains 1.125g fine gold & 1.875g of presumably copper and fine silver.

I normally alloy 18ct at 75% Gold, 15% copper and 10% silver

How much fine gold do I need to add to bring it up to 18ct? Do I need to add extra copper & silver?

I have alloyed gold before but never this way round and I’m going round in circles trying to do the maths!

2

There is probably an online calculator that will do this for you…Rob

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3

According to this: Gold Karat Calculator - United Precious Metal Refining, Inc.

You need 4.51 g of fine gold to bring it up to 18k.

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4

Thanks so much… I can’t believe it never occurred to me that there’d be a calculator online!

5

If anyone is interested, the math works out like this:

(1.125 + x) / (3 + x) = 0.75

where x is the required pure gold to add.

This works out to x = 1.125 / 0.25 = 4.50 g

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