This is a great thread as it’s filled with helpful information.
First, to really get into the “why’s” is way above what my feeble artist brain can explain (let alone understand) but we are very lucky that the forum has engineers, physicists and material scientists who have explained this concept in the past.
If you search Eutectic Bonding within the forum you’ll find your answers. There are a number of threads explaining Eutectic Bonding in Orchid. In a nutshell, some metal combinations like silver and gold when they are touching and heated, lower the metal temperature of both metals at the area of contact.
Jim Binnion does a great job of explaining it here. It’s what makes Keum-Boo and Mokume work.
On to the actual question how to solder a gold setting onto a silver base. As many are saying it’s not that hard, but you’ll need to practice first Julie. That sucks when using gold because it’s expensive to practice with. Maybe you can design some test pieces that will also be finished jewelry so you’re not wasting materials.
Back when I first saw that gold and silver fuse easily I was completely caught off guard as I had no idea that would happen. Then for a while I decided to push it and not use any solder. Just fuse together silver and gold. That worked but it required way too much concentration to be practical, so I went back to silver solder to connect silver and gold components. I did try using gold solder, but my success rate was less, so I stuck with silver solder.
Lots of people solder silver and gold together. It’s not that hard, but there are some issues that will be resolved by hands-on experience.
Hope that helps!
Jeff