leatherback wrote:

Is it a crack that was formed AFTER the pot was backed? It looks to me like a crack that has been there already. In te latter cse, it is not a crack anymore. and you need not worry.

Is there glaze inside the space? Or is it really split

It is hairline and difficult to see into it but I think you are right about it being there already. I do not believe it was cracked afterwards.

Orlando wrote:

The pot cracked during firing. I would contact the seller.

Not possible.

Ivan wrote:

Get some ceramic glue. A brand name around here would be Gorilla Glue, but something that says it glues every thing. Put on some plastic gloves and squeeze a drop into the crack, then another, then another until you have the whole crack glued. That will keep it from expanding, and keep water from getting into the crack and freezing.

You could get the same result without gloves, of course. Don't.

Your suggestion sounds logical and I have now taken your advice. I've filled it in with glue, in several stages, and you can no longer see daylight through the crack even with the aid of a magnifying glass. Thank you again!