Hold the platinum ring with tungsten carbide- or platinum-tipped tweezers. Place a few layers of tissue between the tweezers and the ring to prevent scratches.
Cover the centre stone with fire-coat solution. Wrap it with wet tissue to protect it from the intense heat.
Use 1,700 platinum seamless repair solder. Preheat the inside of the ring, holding the torch below the joint. Position the torch so that the area just beyond the flame’s inner cone is at this location, then move the torch to a position above the joint, directly heating the joint and solder.
Use an intense oxidising flame for soldering platinum cobalt
Pull the torch back as soon as the solder melts and flows into the joint. The flame must be intense, as the wet tissue and carbide-tipped tweezers act as a heat sink and pull heat away from the joint.