In my classes, we do this kind of soldering everyday, numerous
times, and I can give you some tips.
Your torch: That “Little Torch” is NOT my favorite, especially for
heating large areas evenly, and that is your goal with the 1 x 6 in.
piece you are making. A Presto-lite, or acetylene torch, with a
large tip is what you need. High regulator pressure. It generates
some serious heat, which silver of that size will need, but with a
softer, bushier flame. You want to heat evenly, by fanning that flame
back and forth quickly. Silver is a great heat conductor, and it will
"steal" your heat. Don’t be stingy with the heat!
For overlay work, soldering 2 plates of silver (or gold) together, I
would recommend getting both of them DEAD FLAT, having the bottom
sheet being slightly wider than the top sheet on all sides, which
will serve as a “shelf” for your solder. I don’t recommend putting
solder between the layers.
Flux: Handy flux is just fine, but I’d recommend NOT putting it in
beween the layers, but flux the sheets together, as a unit, not
getting the grainy flux between the flat sheets. You need to have
them close fitting.
Solder: Use a MEDIUM solder for this. Hard solder will require way
too much heat to melt, and you may see your silver sheets melt before
the solder does. After drying the flux with a soft flame, place small
solder pallions ( I like to cut small rectangles of sheet solder)
around the edge of your “sandwich”, on the lip of the bottom sheet,
touching the top sheet’s edges.
Heat: I’d also recommend using a large, heavy steel screen, and
heating from underneath, if possible. Also, try to keep your
soldering set-up perfectly level, or you will find that as the solder
becomes a liquid, your pieces may just slide apart, toward the
I think that with perfectly flat sheets, clean and well fluxed, with
plenty of medium solder pieces around the edges, and providing a
robust, even heating should do the trick. Watch for solder flow
around the edges, and inspect the seam closely before sawing off the
"solder lip" on the bottom sheet.