I thought I would do a progressive photo article on making a LARGE round pot.
A few years ago I received a commission for a round pot that would be the biggest I had thrown on a wheel up to that point. The customer gave me the INSIDE diameter and depth that he wanted and explained that he wanted it made from stoneware and finished as some of mine he had seen that I had made in smaller versions.
After calculating out shrinkage for the clay I was using I began the job. This calculation is important as most stoneware clays shrink 10-13% during drying and firing and you must figure out just how big you need to make the pot to arrive at the desired size after all of the firing is finished.
I then needed to figure out about how much clay I’d need for the pot and started to center it on the wheel. I started with 50 pounds of clay which is a job to center!
After centering I began to expand the ball and open it up.
As I expanded the pot I had to constantly keep in mind the size and depth I needed to throw to arrive at the correct commissioned size after drying and firing.
Please note that the bat I am throwing on is 24 INCHES IN DIAMETER!
After I got the walls and bottom the thickness I wanted I then trimmed the rim to the height I needed.
After a couple days of slow drying the pot became the right level of ‘leather hardness’ so I could carefully flip it over and trim the bottom and add some decoration to the sides. On pots over 12 inches I trim in an inner ring that helps support the pot while drying/firing and helps keep it from cracking while drying/firing. Here are some shots of the pot being trimmed.
Pots this size and weight can be a challenge to flip during construction, finishing and drying. Some pots require flipping many times. Try thinking about holding a 24 inch/50 pound pot between two pieces of board out in front of you and flipping it over quickly without dropping it! This is accomplished by two people placing boards on both sides and quickly flipping it as you press on the boards. To make it even more difficult it is often placed on layers of slippery plastic which acts as a slide bearing while the pot is shrinking during drying.
Here are some shots of me flipping a different large oval pot I constructed. The photos explain the process pretty well.
Here are a few photos of the pot after trimming is complete and drainage/wiring holes added and signature. I have also added a band around the outside of the pot rim in a contrasting color of clay as the customer desired. This takes quite a while to do neatly.
The next photo shows the pot coming out of the kiln after being bisque fired to around cone 04. This burns impurities out of the clay, and makes it easy to handle and to finish with stains or glaze. This bisque firing is to around 1,920 degrees F and leaves the clay in hardness and porosity similar to terra cotta pots.
The next photo shows the pot after applying an oxide wash to darken and enhance the color of the clay during high firing.
The next three photos show the pot after high firing to cone 10 (about 2,350 degrees F.) in my gas kiln. This leaves the stoneware clay with only a slight amount of absorption (of water) which makes it fairly safe to use as a bonsai pot and fill with soil which might freeze in the winter. If practicing bonsai in a climate that will allow pots to freeze it is very important that they be made from a good quality clay that is fired to maturity which will leave it ( and the glaze if used) , in a glass-like state that is mostly unable to absorb water. We call this ‘Vitrification’. A vitrified pot is very important in cold climates but lower fired pots with more absorption to the clay can be used in warmer climates where freezing is not a concern. However, quality clays and matured clay firing levels are desired so your pots don’t absorb too much water and leave salts, etc. dried on the outside surface.
You can see some firing marks on this pot where flames were hitting the sides of the pot. This is a great effect which I feel is desirable and I suggested that this be the ‘front’ side of the pot when the tree was potted.
The next two photos are of me holding the pot so as to give you a good finished scale view.
This large pot has been potted with the intended tree for about 3 years now. It is a very large San Jose Juniper. Here is a photo from 2010 winter in storage. I hope to see the tree in a symposium bonsai display within the next few years. The owner says it’s getting close to being ready to show.
Here are a few other photos of customer’s large commissioned pots that I’ve made over the last few years. They are potted with their trees. These are all in the 16 inch to 21 inch range.
I hope you enjoyed this brief view of making a large wheel-thrown bonsai pot.