The problem, John, is that silver-filled is, allegedly, 500 to 1000
times thicker than silver plate. Just testing the outside of a
silver-filled piece with a touchstone will yield sterling silver
results. You'd have to cut into it to find the layer of brass.
Silver-filled, sold by legitimate companies, such as Rio Grande,
contain an outer layer of silver at least 1/10th the weight of the
metal. It can be soldered, formed, stamped, textured, polished to a
high degree, even engraved.
Like gold-fill, it is an affordable alternative to solid though it
does take a bit of practice to learn how to work it. While not a
master smith's, or even a beginner's, metal of choice... Well... Some
of us have fewer choices than others. I'm just waiting for them to
make Argentium silver-fill.