When a ring only needs to be sized up by a small amount, you can easily size the ring by stretching. This is the perfect way to size a plain ring that doesn’t have any gemstones and is made of only one type of metal, as it will save you time and money.
Before beginning, it is very important to check both sides of the ring on a mandrel to be sure that they are both the same size.
You will first want to anneal the metal, as this will make the stretching process ten times easier as the metal will be more malleable and less likely to crack under pressure. It is best to fire coat the ring to protect the finish before annealing. Heat the ring with a soft flame; this will cause the fire coat to seal on the ring. Continue heating to anneal the ring, when the metal glows faintly red you have reached annealing temperature and you can quench the ring in water.
Once the ring is quenched, place the ring in the pickle to remove the boric acid coating. Rinse and dry the ring before enlarging the ring.
The quickest way to stretching a ring, is to use a ring-stretching device. Before sliding the ring onto the ring sizing device, measure it on your mandrel to be sure of the size. Then wrap a small bit of regular paper around the device and slide the ring on top. This will protect the inside of the shank from getting scratched. Pull the lever to expand the splines of the device; this will begin to stretch the ring. As this device applies a lot of pressure, the ring will change size very quickly, so close the splines and remove the ring to check its size often. Don’t forget to flip the ring over and stretch it from the other side to ensure that both sides are sized to the same point. DO NOT work too quickly and overstretch the ring!
Once the ring reaches the desired size, check for any distortion marks. The more you stretch a ring, the more likely it is that there will be signs of distortion. Sand and polish the ring to remove any distortions and return it to its original luster.