Herkimer Diamonds are not the same diamond that you are thinking of. Lets stop right there. They are a diamond found in the Herkimer NY region and are roughly 500 million years old. They are basically a quartz.
Tinning is the art of soldering silver around a gemstone for a quick solution to setting the stone. Other choices are more time intensive, and must be done with careful attention and training. Running bezel, setting and shaping stones is very tedious work and you need lots of practice and training to master these skills. Tinning however can be done quite easily and anyone can learn to do it in an afternoon, especially if you have ever had to solder anything. Check out my quick video on tinning, I time-lapse an hour of work into less than 2 minutes!