You can remain involved with the project even after a Stolperstein has been laid – for example by cleaning the Stolpersteine. This means to check on the Stolpersteine regularly, see if it has become dirty or damaged and polish its bronze surface. Without being cleaned ever so often, the brass changes its colour and darkens – cleaning it with metal polish helps to prevent this.
This short video by Stefan Ringelschwandtner gives helpful advice in how to clean Stolpersteine best. You can see it here.