So I never take on repair jobs any more because of past years of doing them and constantly running into issues. Would much sooner take on fun projects. 
Well, recently I offered a wedding band (sizing up from a 6 to an 8 for a friend) Ring had been carefully removed using a ring cutter because of an injured finger
Multiple issues as I had to create a similar piece of stock using 18K 5-1/2 mm with a 3mm overlay of platinum, just under 2mm in thickness.
I struggled to make the insert ,but finally got there, then all I had to do was fit the new section and solder . My lowest easy platinum 1000 was not working (afraid of melting the yellow) so I opted for 18K white medium which worked like a charm on the first join, followed up with 18K yellow easy to fill the gold portion.
I noticed when heating the ring that the two metals in the ring expanded a lot somewhat similar to a bimetal thermostat strip so when attempting the second join Wired down the band solid before soldering
After several failed attempts I nearly lost it as was on the second day.. I should have posted this at that point and called for HELP!
Frustrating as heck because the ring when heated just moved in contortions and always enough to prevent the soldering… Incredibly strong spring that even my tightest binding wire could not handle
After some sober deep thinking I devised a new plan and this worked well enough to write about it
I found a small stainless steel hose clamp opened up a section to expose the area to solder and used a round edged diamond burr to form a section inside to keep the ring in place when the clamp was screwed tight … Once the ring was secured I tried soldering and even the clamp gave way the first round to I repositioned the ring and the next time managed to solder the joint successfully
I am again sharing this story because I had never thought of this strategy before and it just might come in handy in future when soldering tough materials like white gold bands?
This metal combo was certainly a challenge that I won’t soon forget. A tricky sizing but ended up taking a crazy amount of time. (Yes, I tried annealing the platinum but perhaps couldn’t get it hot enough given the fact it was surrounded by 18K yellow.)
The last detail was two parallel rows of a deep mill grain type line on each platinum edge … I used a small diamond point tip in my hammer handpiece to replicate it … Its close