Just going through my bag of coins and saw that I had a lot of 1963 and 1964 Roosevelt dimes I research this and it looks like these dimes have about 2.25 g of silver with a make up of 90% silver and 10% copper, does anyone know how to make sterling silver from these dimes? I would imagine I would have to add a little bit of fine silver to bring up the quality to Sterling.
Coin silver is a 90:10 alloy of fine silver and copper. The extra copper vs Sterling allows the coins to be a bit more resistant to wear and tear banging around in pockets and purses. You should be able to find the calculations needed to add fine silver to coin silver to make it equal to sterling which is 925:75 once you know the weight of the 90:10. This is one of those exercises that might be interesting to do, but it is not a regular shop practice. It is kind of like making solder. Good luck and have fun…Rob
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I thought that I could derive this formula, but it eludes me. I had to take Algebra twice to pass the Regents test. Can anyone help?..Rob
This answer do not make sense, since he never told how much his dimes weighed.
We can calculate the percentage, but not the actual value, until we have a start weight.
Right?
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Here you go.
Multiply the weight of copper by 12.333 to find the total pure silver amount needed for .925 silver.
If you have 10g copper and 90g silver, you need 123.333 silver (33.333 more silver) to make 133.333g 925 silver.
I deleted previous posts as this is simpler and more accurate.
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Thanks!..Rob
They are worth more as dimes , you can trade or sell them instead of raising the silver content .Just trade or sell .do not try to alloy in fine silver .It can be done but it would be a tremendous waste of time and by reheating you will probably ad impurities into your melt . Don’t bother !
Fifty year veteran of the trade .
Chuck
Did you know you could sell the dimes for more money then the silver is worth? Thus you could but the silver that you need without the need to melt a dime that is sixty years old. Which by way is as old as I am. Seriously, people buy coins for more than the dime is worth and more then spot silver prices. Check eBay and see for you self. If you’re still determined to melt the coin well you have every right. 
Blessings and best wishes 