When knife crime rose across the United Kingdom, the British Ironwork Centre came up with an idea. Working with local police forces, the Centre built and placed 200 deposit boxes around the country and ran an amnesty campaign. One hundred thousand knives were anonymously surrendered, some still with blood on their blades. These were then shipped to artist Alfie Bradley, who blunted them, inscribed some with the names of young knife-crime victims, plus messages of regret from ex-offenders. All 100,000 weapons were then welded together to create the Knife Angel—a 27-foot-high angelic sculpture with shimmering steel wings.

When I stood before…