/sci/ - Science & Math

I started growing some CuSO4 crystals two weeks ago using the method in this video https://www.youtube.com/watch?v=FKCS1DvORug . I prepared a saturated solution and then I placed it into different containers, some in plastic flasks and the rest in glass jars, in which I placed the seed crystals. I left everything unattended until recently. The crystals have grown, including the ones that have formed at the bottom, and most of the water had evaporated, so the CuSO4 had started to form on the walls of the containers. Now my question is, how did the crystals start forming on the outside of the jars as well, while the holes were covered with cardboard? Can the vapors of the solution pass through the cardboard? I noticed only a little CuSO4 on the cardboard and this only happened to the glass jars. Also, why is it easier for crystals to form on glass than on plastic? I noticed that when using a glass jar, the crystals formed much faster, which I guess is why this didn't happen to the plastic flasks.