No, we usually don’t stretch them, although very occasionally will stretch a plain band up by a tiny amount. It is risky and makes the ring thinner, so we’d prefer not to.
No, what we do is, generally, cut the ring and either remove enough material to size it down, or add enough material to size it up. The length of material necessary to raise or lower the size is just over 2.5mm per, or the thickness of two dimes. When asked what we do with the gold that we cut out of down-sized rings, this number will help to reassure customers that we’re not making out like bandits on each sizing; most of the cost of sizing is in the labour. It takes time to do it right.
The simplest sizing is one where the ring is being sized down, is still in good shape, and the back of the shank hasn’t been thinned out by wear. The ring is cut and filed so that there will be no obvious seam, then closed up, maintaining the original, circular shape as much as possible. It is then soldered, cleaned up, and polished. Would that it was always that simple, but that’s the basic gist.
Sizing the ring up involves opening the ring to the correct size, ensuring, once again, that the basic shape is maintained. The opening is then filed so as to present two parallel sides, a piece of gold filed to fit, and the repair soldered and finished as before. The sides of the opening need to be parallel so that the new piece will be held in place while soldering, otherwise it pops out as it’s heated and burns a hole in your shirt. Don’t ask me how I know. I am, of course grossly over-simplifying the process, but I haven’t got all day.
Where the process gets complicated, is when the back of the shank (the ring part of the ring) is so thin that, to size it up in the normal manner would render it ridiculously thin. This can be due to wear, or built in to the structure of the ring by shabby manufacturing. If the latter, little can be done to improve it, but if it’s just the back bit of the ring, then extra material can be removed, out to where the shank is a bit thicker, then a more substantial piece of new gold can be soldered in. We try to send stuff out looking better than when it came in.
If there is so much wear that the ring is thin more than half-way around the shank, then a full shank replacement will be necessary, but that’s a story for another day.
Just a note about solder. When we talk about solder in the industry, we’re not speaking of lead solder, which is the most common type that people think of. Horrible stuff used on electronics and copper plumbing. Our solder is actually karat gold (10K, 14K, 18K) that has been alloyed in such a way as to lower its melting point. Properly used, it makes an invisible joint that is as strong as the original material.
Thus endeth the lesson. For more pedantic fuckery, stay tuned.