Post 76 Concrete bonsai pots

I was reminded recently of my first steps in bonsai pot making was actually many years ago. While it has only been more recently that I've ventured into ceramics that first step was taken with concrete.

So I've been out to scout around and find those old pots. I was pretty sure some were hiding in one of my 'boneyards' around the place and sure enough there they were covered in a age of decaying eucalyptus leaves. We've been here for 10 years and so these pots must be at least 15 years old, made at a time when my trees were smaller and so the pots are of a fairly modest size.

This model is about 250mm long. I recall looking for some way to get some shape into the wall design and hit upon using timber skirting board. It comes in a variety of profiles and height, ideal for making moulds like this. I simply mitred up four pieces and used a piece of wire to hold it all together and in shape. The concrete mix was about 3 coarse sand to 1 cement and only just enough water to moisten the mix, with no 'free' water. After oiling the mold then, bit by bit then I rammed the mix into the mold - floor and walls and then smoothed off the inside.  After a very short time it was strong enough to take out and immerse in a container of water. As they say concrete continues to get harder and harder over time. As I recall most things would grow in these pots, well except azaleas which prefer acid to alkaline conditions. 

This is a detail of the feet which were set in place as soon as the pot was released from the mold.

 This one was a little more ambitious. To make this mold I used a bonsai pot I had and coated it with many layers of casting latex, then a concrete surround to support the latex. Reverse that when set and follow the same rammed concrete procedure, into the latex mold. The mold included the feet so did the whole job in one go.

The latex is never going to work with clay but anyone looking for an easy way to make a ceramic pot mould might like to try timber. You can also add all sorts of things to a cement mix, like poplystyrene particles to lighten the material, which would be great if you needed a big grow pot. Leaving a pot immersed in water for a good period will get rid of most of the alkalinity that will initially come out of the concrete.

Post 75 New pots

The bow tie clamped pot of the last post went into the kiln with 4 others - yes squeezed 5 in this time. Here are the other 4.

 

 Pot 27 has been hanging around for a while, given I'm now into the 50s. It was an early unflanged Sabani and has finished up at  344 x 238 x 79 in a green toned off-white satin glaze.

 Pot 38 Is similar as 27 except that it has the rim flange. After having made a few of these it is clearer now how to keep them in the shape I want and this one has worked well. Glazed in a dark slate satin glaze and final size of 357 x 252 x 79.

 Pot 42 This Wasen pot is the first one that I've tried the 'planking' wall texture with the squared rim flange; quite boat like. Size is 420 x 238 x 79 and the glaze is a satin mint green colour that I've used before but this time took the copper from 2.25. to 3%. The deeper colour on the highspots works well. Here's a more detailed shot.

And the last for this firing is a Bekabune , Pot 45, in antique parchment satin. Final size is 350 x 257 x 64.

Post 74 Bow tie repair

The results from the bow tie repair experiment are in and here are the pictures!

From the outside of the pot this was what it looked like at bisque and the following shot is from the inside with the bow tie clamp in place.

As I was glazing the pot I thoroughly wet the area of the crack and then put glaze in the clamp cavity and on the tie before putting it in place. Then after a little more water along the crack followed with dilute glaze to encourage some to flow into the crack face. At the very rim of the pot this seemed to work quite well with the glaze acting as a good bonding agent.

 And from the inside you can see that at the position of the clamp it is quite sound.

But equally obvious is the way the crack propagated and opened up where it wasn't clamped.

For a pot that would otherwise have been junked it's been a useful experiment. The clamp was about 2/3rds of the wall thickness and was good enough to do the job on its own at the rim. If this happened again I be tempted to try to save a pot by placing these clamps spaced about 30mm apart for the full length of the crack, and instead of trying to disguise the flaw from the outside of the pot actually set the clamps for the full wall thickness. And then the clamps could be made of stained clay so they finish up a different colour. Hmmmmmm.... I'd better stop now before I go and deliberately crack a pot!