Silver-filled is a new layered metal that was introduced during the recent surge of silver prices during the recession. It is not an alloy because the metal content is not the same throughout the material. その代わり, the sterling silver is all on the surface. Silver filled is either 5% または 10% sterling silver by weight fused with heat and pressure to a brass core. This metal is fairly new so it is not standardized in the US. Since silver-filled is a layered metal it cannot be cast. The silver layer is much thicker than silver plate but this is still a much lower quality product than solid sterling silver jewelry supplies and alloys. It will tarnish and it should only be soldered with precision equipment and special training. Now that the price of silver has come down from past highs the metal is less common in the market. There is no legally approved quality stamp standard for silver-filled at this time. しかし, some use the stamp .925 SF, which can be misleading.