Rings with stones cannot be stretched on a mandrel because of the stress this puts on the stone. There is a danger of breaking the gem, or at least popping it out of its setting. When stones are involved, and if the enlargement is slight, a tool like the one shown at figure 13.8 is recommended.
The device has a number of dies of different shaped grooves that mimic the cross section of the ring shank. Select the one that corresponds to the ring being stretched and attach it to the vertical post of the machine. The ring is then forced against this to locally “forge” the shank. As mentioned above, the action exchanges thickness for length, pressing the ring in such a controlled way that the change is unnoticeable. Of course there is a limit to the stretching that can be done this way, not only because the metal hardens at it is stretched, but the shank could eventually be made too thin.
If the ring contains heat sensitive stones then this complicates soldering. Amber, coral and pearls are so sensitive that such stones need to be removed if a normal soldering flame is used. Other sensitive stones should be taken out if possible. If this is not possible, then they need to be protected against heat. Numerous possibilities have been recommended, all of which are based on the concept that the stone is packed in moist material so that the heat of soldering boils the water instead of being transmitted to the stone.
Sizing Down Plain Bands
When a basic wedding band or similar ring needs to be made a little smaller, the first method of choice is to compress it. Like its corresponding partner, stretching, this is fast, efficient and the least intrusive process. And like stretching, it can only be used when the change in size is small.
If the ring is made of several metals, for instance of white gold and yellow gold, this method is limited and might even result in breaking the two metals apart because they have different rates of compression. If the outer surface of the ring is faceted, chased or engraved, protect it by putting a copper band around the ring to absorb the stress at the point of contact figure 13.12b). A variation on this device, shown in figure 13.12c uses a bushing to protect the ring’s outer surface.
Sizing Down Gem Rings
The stone or stones are taken out and the ring shank cut, again exactly where previous joints have been made if there are any. Remember to check the inside of the band for hallmarks and engraving and to work around them. The shank is bent so the ends come together to make a tight seam, and here again it is important to file the surfaces so they make a clean joint. Failure to do this will make an imperfect soldering that will leave irregularities or pits; in the process of filing these away it is easy to make the shank too small. In the case of thin shanks, file the two butting surfaces at an angle to increase the surface contact and thereby make a stronger joint.
With larger stone settings and delicate ring heads there is a danger that the head of the ring will be bent out of shape and deformed on any of the methods described above. The shanks can break off at the head of the ring or from its shoulders where the solder joints are stressed. It also happens sometimes that a thin shank is simply worn so thin it can no longer be repaired with an isolated joint.
No matter what your needs are for gem ring enlargement, come in a we will take care of them all.