Wondered? Since people put wet shirts and towels over their carboys sometimes to get a few degrees below ambient, would the same hold true for a large terra cotta pot with a carboy in it?
I was thinking that if it would hold true, my pottery friend could help me make a really nice looking cylindroconical. I imagine a double walled vessel with the inside of the fermentor glazed like a sink/tub, and the remainder of the project unglazed terra cotta or other earthen slip. The inside between the two would have supports connecting the two walls together and strengthening the vessel. At the top would be a seperatley fired lid with glazed interior side. I think I could find a nice fitting to connect a ball/butterfly valve in the opening at the bottom of the fermentor. The outside of the vessel would have design molded into it (barley,grapes,wheat,etc..)
It sounds pretty elaborate, but my friend tells me it is more than just possible. He says even on the scale I would like to build at (16.5 gallon) that it is doable, "If we can find a big enough kiln," so the man says lol. The thing both of us don't know is if it will cool like the terra cotta water coolers and filtering units we have seen advertised. They claim 10-14 F degrees below room temperature on a 5 gallon system. This is the only reason I have imagined doing this in the first place, so if you know anything please comment because it would really help in my project.