Can sodium hypochlorite soak all the way through an unglazed ceramic cup and bleach blue paper wrapped around the outside of the cup? My question is regarding the ionic properties of sodium hypochlorite in house hold bleach. There is a debate among potters whether bleach will kill mold growing on a porous ceramic cup. It is my understanding that sodium hypochlorite cannot penetrate a porous surface of fired clay. Someone did an experiment where they put household bleach in an unglazed cup and allowed it to soak through. There was blue construction paper wrapped around the outside of the cup and the paper turned white after a while seemingly from bleaching. So my question is this: If the ionic properties of sodium hypochlorite will not allow it to penetrate through the cup to the outside, then how did the blue paper wrapped around the outside of the cup get bleached?
It is not the ionic properties that control the diffusion. Diffusion is a fundamental property of molecules dissolved in a liquid. A bleach solution stored in an unglazed container can potentially diffuse to the wall. The pore size of the material will mainly control the rate of movement of the fluid (viscosity, surface tension etc.) If the pore size and the connectivity channels are very small it will take ages to wet the wall under atmospheric pressure.