working out what ct i have????

[CJ57]

Hahaha......enjoy your wee faint Caroline, this won't happen often

We can but hope Jill

[susieq]

If I have 30g of 12ct gold and 25g of 9ct gold what ct gold do I end up with????? T.I.A

This took me right back to being in a maths lesson with my "if you didn't understand the question the first time you obviously weren't listening so I'm not going to repeat it" maths teacher. Anyone else remember having to formulate an equation to work out how long it took a bath which held X gallons of water to overflow if water came out of the taps at Y gallons every 6 minutes and emptied down the plughole at Z gallon every 5 minutes? Or am just showing my age ...
Susie

[SteveLAO]

I think I've done this one before, but anyway....

30g of 12ct contains 15g of pure gold and 15g of other metal (30 x 0.500)
25g of 9ct contains 9.38g of pure gold and 15.62g of other metal (25 x 0.375)

So you would have a lump of metal, total weight of 55g (30+25) and containing 24.38g (15+9.38) of pure gold. This gives you apx 440ppt of pure gold in the alloy, or apx 10.56ct in old money.
But as previously said, you'd still only get a 9ct hallmark on it!

[ps_bond]

This took me right back to being in a maths lesson with my "if you didn't understand the question the first time you obviously weren't listening so I'm not going to repeat it" maths teacher. Anyone else remember having to formulate an equation to work out how long it took a bath which held X gallons of water to overflow if water came out of the taps at Y gallons every 6 minutes and emptied down the plughole at Z gallon every 5 minutes? Or am just showing my age ...

Fair point, but the teacher was being paid. Ask the question once and get shown how to work it out, fine; then to ask it again without bothering to try, well... Jewellery requires maths in some areas. Geometry and arithmetic mostly, rarely simultaneous equations and unless you're looking at more industrial processes then it's extremely unlikely that differentiation, integration or complex numbers will feature.

Give a man a fish, feed him for a night. Teach a man to fish, feed him for the rest of his life.
Alternatively: Set a man a fire, keep him warm for a night. Set a man afire, keep him warm for the rest of his life...

And given I've just been playing with numbers involving fluid flow rates and volumes - it's quite familiar.

[Paget Jewellery]

thank you everyone for your replies I know I presented a similar equation last week, I understand the equation and what ct I end up with but I have no ratio to put it towards is there a table or graph I can download, i.e 1g of 9ct =?? of 24ct, 1g of 18ct= ?? of 24ct, I gram of 14ct= ?? of 24ct, if not someone should make one, and show what in (g) i.e .042g of a (g) is 24ct if that makes sense, show the conversions

[Paget Jewellery]

yeah cheers I mean I'm all up for learning, if there's anything I've learned then it's jewellery requires time, learning and effort alongside research and information gathering...

[Paget Jewellery]

steveLAO that makes perfect sense thankyou!!! and the penny drops....

[Icarleug]

Since 24ct is pure gold 9ct contains 9/24 parts of gold.

So 30g of 12ct gold will contain 12/24*30 = 1/2*30 = 15g pure gold if you refined it.

Since you planned on melting it anyway it would probably be better to figure out how much other metal to add to the 12ct to make it 9ct.
In reverse that would be 15g pure gold made into 9ct = 15*24/9 = 40 g. Subtract the 30g you already have and you get that you need to add 10g of other metal to make the 12ct into 9ct.
Sadly though, metallurgy is not something I have done, so I can't help you with any ratios of silver and copper (or other metal depending on what you started out with).

As a formula for Excel or similar you would use =(A1/24*B1)
Put carat in A, weight in B and the formula in C (Adjust the formula for row numbers)

To summarize:
Gold Weight = Carat / 24 * Total Weight
Carat = 24 * Gold Weight / Total Weight
Total Weight = 24 * Gold Weight / Carat

/Andreas