I worked on a large vessel over the course of two days and I'm posting step by step of the upper half to finish. The final size is 43 x 43cm.
All larger work like this I do using a coil and paddle technique native to Karatsu, and it is very effective for making even large pieces thin, light, and strong.
Here it is after resting overnight. I do this to let the bottom section firm up, so it can support the weight of the top. Wet towels draped over keep the top edge soft so work can continue the next day. If it gets too dry the connection will be bad and it will crack and split.
After one coil added the following morning. Here you can also see the anvil marks on the interior:
Then I just add coil by coil, pinching it up, then paddling to shape and compress, repeating the process until I get the height I need.
Here I finish the mouth by folding the lip over on itself a couple times and compressing, then add some decorative lugs to the shoulder. Historically, these would be bigger and beefier to be used as tie downs for a cloth cover to keep pests out of whatever was being stored in the jar.