When silver is heated to near melting temperature its crystals move apart, opening up microscopic spaces. Soldering uses an alloy that melts before the silver does and then flows into the spaces in the silver, so that the solder actually becomes part of the piece of work.
What you need for soldering to work.
First of all, you need a clean piece of work (dirt will stop the solder from flowing) with a good fitting join. If there is more than a very thin hair-line gap between the two pieces of metal then the solder will flow into the two pieces and not hold the join together.
Secondly, you need flux, a chemical that makes the solder flow when it's melted. If you don't add flux to your work then the solder will just ball up rather than flow into the join.
Thirdly, you need the right sized flame. Solder is melted by the heat of the piece of silver, not by the heat of the flame. If you don't use a torch with a big enough flame then the piece of silver won't heat up to the temperature needed, but then again if you use a torch with a flame that is too big on a relatively small piece of silver then you risk melting your work! I've got two hand torches that I use in classes - a small butane torch that I use for small pieces of work, and a larger butane/propane mix torch that I bought in from my local B&Q that I use for larger pieces of work. I've also got a more professional torch that runs on propane gas bottles, but I don't need to go into that one here.
And of course you need some solder! Use just enough to fill the join. It's quicker to cut a new smaller piece of solder than to file off the excess solder afterwards!
When you heat the silver the flux will first of all bubble up - the piece of solder may "jump" off as the flux dries. If it does (and it does it to everyone!) just turn your torch off and move it back again!
|The flux has dried and bubbled. The solder is inside the ring and the heat will draw it through the join.|
|Nearly at soldering temperature - the flux has taken on a glassy appearance|
|The flame was on the outside of the ring. As the solder flows towards the hottest part it flowed through the join to the front. If I can see a line of solder on the front of the work I know that the join is strong.|
|Oxidisation forms on sterling silver when you heat it and this needs cleaning off in safety pickle - it will then take on a white-ish appearance.|
A couple of trouble-shooting tips for you:
- If the solder has jumped to one side of the join rather than through and across the join then you have probably heated up that side more than the other as the solder will flow towards the hottest part of the metal.
- If the solder has balled up rather than flowed across the join then you have either directed the flame to much onto the solder itself rather than onto the silver or have not used enough flux.