Why do terra cotta flower pots turn white?

I just wondered this while looking at two potted aloe plants I have. Their pots used to be just red clay, but over time, they've mostly turned white. Almost looks like someone painted on them. Oddly, my potted cactus's pot has never turned white. Why does that happen?

Why do terra cotta flower pots turn white?
It's salt and mineral deposits leaching out of the soil and seeping through the terra cotta. It may be on the aloe pot and not the cactus for a couple of reasons: You may be watering the aloe more, hence more deposits. Or, the cactus was planted in a pot that was glazed on the inside, but not the aloe.



This happens to terra cotta pots that aren't glazed.
Reply:Salts come out from the pot when watered over time. You can re-pot the plants and scrub those pots, they'll turn back to the original colour again.
Reply:I think it is lime scale from the material in the pots. It leaches out when yo water plants.
Reply:This is called efflorescence. This problem happens in clay brick and concrete as well. The salinity in the dried product leaches out over time. There isn't much you can do about it trying to cure the problem has never been solved.
Reply:They use calcium chloride to chlorinate potable water and when evaporation occurs the water and chlorine evaporate into the atmosphere leaving the calcium behind as a salty residue. Fertilizers and natural occurring salts in the soil also do contribute to the scaling to some degree.