melting silver coins

Coin silver is not going to work well for jewelry, it has a higher copper content than sterling.
My son & I made a ring, it turns black on his finger.

About the same level of surprise value for that as finding rust on bare iron at the seashore. If it isn't sealed in something airtight, and it's made of (other than sterling) silver, it's going to turn black. Just because of what it is.

American coin silver is 10% copper. There is no problem with melting it down other than silver's tendency to absorb oxygen from the atmosphere while molten. On cooling it gives up the oxygen which then may cause porosity in the silver. It makes jewelry that is wear resistant, but will tarnish more readily than sterling silver.
Randy

The problem with silver absorbing oxygen is dealt with when copper as added to silver, so that issue is of no consequence. Coin silver melts much better than pure silver. Use a reducing flame when melting to avoid burning the copper, which can lead to porosity. (American) coin silver is alloyed @ 10% copper, 90% silver as has already been stated. Sterling silver is 92-1/2% silver, 7-12% copper. Considering the alloying is accomplished by weight, not volume, and copper is considerably lighter than silver, there is a much larger volume of copper in coin than in sterling silver, but it generally does not present a problem. Those that have coin turn color on their hand would likely also have the same problem with sterling.
There is nothing wrong with using coin for jewelry, it's been done through the ages. Just don't mark or otherwise represent is as sterling. In order to do that legally, you'd have to raise the silver content, and that takes a lot of pure silver.
Harold

Silver is not that much denser than copper. The specific gravities are: Copper - 8.93 Silver - 10.49
Given the above, a 90/10 ratio by weight of silver/copper would be a 88.45/11.55 ratio by volume of silver/copper.
To raise a given amount of coin silver to a 92.5%/7.5% ratio by weight, add 1/3 by weight of pure silver to the melt. eg melt 3 oz of coins and 1 oz of silver will raise the ratio to 92.5%/7.5%

Their value as coins will rise with time. Their value as a poor silver ally will not. Put them in a box in the attic and leave them to the kids in your will!
Mark Rand RTFM

I used to make lots of jewlery from coin silver back in he 70's. Used many, many silver pesos back when each peso were 8 to the dollar. I'd melt them down using borax as a cover flux and a bare carbon arc gouging rod as a stirrer. I'd then pour the silver into cast iron muffin pans. When it cooled enough to be good and solid, I'q quench in dilute sulfuric acid/water pickle bath. The pickle bath would remove the borax and any copper that was on the surface. Them were the good ol days!

snip-----> That's correct. I guess what I was trying to say is that it's rather deceiving when you have coin silver and want to elevate it to sterling (only a 2.5% increase), it takes a considerable amount of silver (1/3 of the beginning weight, or 33-1/3%) to raise the content to legal specification.
Where weights versus volume really come into play is when alloying 10k yellow gold. By volume, gold is an almost insignificant portion of the alloy.
Harold

I'd question that assumption - on the basis of eBay sales.
However, you can buy $1000 face value bags for a little over melt: This place has them: So older US coins are indeed a good source of silver - for silver's sake.
Main problem is oxidation during the melt. Cover them in a nice thick layer of borax, and don't mess around when the stuff is hot.
Given that, its a breeze to melt. Throw in a few .999 silver rounds (less than $7/oz) to raise the alloy closer to sterling - but don't fuss about it. Its not that important.
Coin silver is a great source of silver metal. That's the reason I got into numismatics in the first place. Just make sure you don't melt that one-in-a-thousand super-rare key date coin.
I get a yellow (copper-rich) patina on my castings when I cast coin silver, but it polishes out easily. If you are cutting or machining it after casting, then no worries. Get it hot enough. Freezing in the sprues can be a problem if you're impatient. Can be gluggy when molten - stubborn to pour. Casting under gravity (alone) can be difficult. Centifugal or vacuum is generally preferred, but plain gravity can be used to make billets (ingots) or less complex shapes. I like to cast (under gravity) a billet shape, then machine it to final specs.
Black residues are no more troublesome than with sterling. Easily removed.
Understand you'll waste a bit in crucible residue, sprues, flash, burn-off, machining swarf etc.
But - hey - silver is cheap.
Go for it.
-- Jeff R.