Take a rod of ivory and melt a blob about the size of a grape. Let it form a "skin". Have a strip of silver foil (you can also use leaf, but the foil gives you more intense webbing, etc...) and pick it up with your tweezers. Touch the foil to the blob of glass, then wind it around and cover the whole blob - just take off any excess. Burnish it in really well (I just use my tweezers and rub them all over the silver to make sure it's attached well). Re-introduce into the flame and melt it in - the silver will burn off. Get the blob evenly heated, then take out of the flame and pull your stringers.
Silvered ivory stringer is a lot more brittle than normal stringer, so just be aware of that when you go to use it.
Hope this was clear! Have fun!