Does rubbing Vaseline on the sides of the growing bowl really prevent crystals from forming there?
No, but it does stop them from climbing up the sides of the bowl as they commonly do. The following picture shows crystals working their way up the side of the bowl: What happens it that a spot on the edge of the liquid creates a few seed crystals. These are close enough together so that by capillary action they draw some fluid up into their structure. This wet zone evaporates creating more crystals, which grow partly upward. the wetting and evaporating process continues with the crystals literally pulling themselves up by their own bootstraps. This process can be demonstrated by placing a tall piece of porous pottery in a dish of growing medium. The best growth will occur on surfaces that are rough because they have been broken. Does Vaseline prevent crystals from climbing up the side of the bowl? Yes. The following picture shows the edge of a dish that had one half of its surface coated in Vaseline. The area on the left had the Vaseline and shows how it stopped the crystals from work
