وَالنَّجَاسَةُ إِذَا أَصَابَتِ الْمِرْآةَ أَوِ السَّيْفَ: اكْتُفِيَ بِمَسْحِهِمَا.
Translation: If impurity reaches a mirror or a sword, wiping them clean suffices.
Mirrors and polished swords illustrate smooth non-absorbent surfaces. Wiping can remove the actual filth completely.
If a surface is porous, cracked or retains impurity beyond the reach of wiping, the same result cannot be assumed.