The World Federation One Stop Fiqh

Ruling 164

An impure object does not become pure until the intrinsic impurity is removed from it. There is no problem, however, if the smell or colour of the impurity remains on it; for example, if clothing that has become impure with blood is washed with water and the blood substance is removed but the colour of the blood remains, the clothing is pure. And even if the colour of the blood could be removed by using a cleaning product, it is not necessary to do so.