Compared to pure silver, a silver alloy called sterling silver is

The given blank can be filled with harder and more durable.

Explanation:

Sterling silver refers to a silver alloy comprising 92.5 percent by weight of silver and 7.5 percent by weight of other metals, generally copper. Fine silver like 99.9 percent pure silver is comparatively soft, thus in order to increase hardness and strength, silver is generally alloyed with copper. However, sterling silver is vulnerable to tarnishing, and elements other than copper can be utilized in alloys to minimize tarnishings like zinc, germanium, silicon, platinum, and boron.

hard and durable

sterling silver refer to a type of silver which has purity or more correctly finess,  92.5% silver by mass.the remaining 7.5% is copper and because of hardness it is being used in coins jewelry etc