Tuesday, 30 April 2013

Post 89 South West USA - trees and pots

Just back from a quick run around the national parks of the SW of the USA, from Phoenix, Grand Canyon, four corners area and around to Bryce and Zion. Stunningly beautiful scenery in a very arid landscape.

The Colorado Plateau sits over the intersection of Colorado, Arizona, New Mexico and Utah and many of the parks take in the mountains and gorges created out of the weathering of this great plateau. The picture above is a typical scene, if not a little greener than most.

The dominant trees in this great area are pines and junipers, more specifically Pinion (pronounced pinyon) Pine and Utah Juniper. These two species successfully occupy the same territory in areas where rainfall is as low as 200mm or less and moderate altitude. They  like it cold and dry and commonly while they commonly reach 3 to 4 m in protected areas, depending on conditions they will normally have suffered some level of natural bonsaification and will oftern be much shorter.

This picture shows the two right next to each other. Along the route we took there must be countless thousands of square kilometers of this dominant mixed forest.

This is a close up of the Pinion needles, very compact and quite heavy needles (in pairs), looks like a natural for bonsai culture but replicating the right condition in all but close to its natural range would be challenging. The pinion produces an edible nut which has been harvested from the earliest time of human occupation of the areas.

In higher rainfall areas the mighty Ponderosa pine takes over and what a mighty tree they are too.

This is what their needles look like, a very different picture from the Pinion. Surprisingly I did see a number of Ponderosas in exposed low rainfall areas that had taken on a nice small stature and shape, but its no prospect for a small bonsai with needles like that.

This next one is the Bristlecone Pine, possibly the species that has the oldest living trees - up to 5000 years apparently. I didn't see any of the really old live ones but found this young one with a few friends out on an exposed point at Bryce.

Up close the needle structure is even more compact then the Pinion. Pardon the glove but when I took the shot it was zero C and there was a blustery wind - I've never been quite so cold, but then when you live in a temperate climate......The needles of the Bristlecone grow in bunches of 5.

I'm not sure what this one was but longer and at the same time quite heavy needles.

The trees on the trip were quite instructive and inspirational. The forces of nature in the harsh conditions in which they survive result in a natural shaping which is at odds with much of the formal structural conventions of bonsai, but at the same time beautiful in their own natural way. Immitation of these natural shapes in bonsai would result in very attractive trees.

Next post I'll show you some Junipers.
And the other interesting theme of the trip was a pottery one - yes the pottery of the ancient pueble cultures that reached their peak 800 years ago. Beautiful patterns and natural earthy tones for great composition. 

Tuesday, 16 April 2013

Post 88 Fitting feet

How to fit feet to pots is really no great mystery or significant IP to be protected. The method is no different to that for joining any clay pieces. This is how I do it.

 First roll out some clay to the required thickness.

Then with a template of the foot design I want to use I roughly cut out pieces for the feet and then set them aside to dry a little. This foot template is for a square semi cascade pot.

I usually place the pieces on a piece of gyprock or drywall sheeting. If you do this and have a couple of small pieces the same size, the clay is easier to turn and get even drying. I like to dry the clay on the wall sheeting and in contact with the air for 4, 5 6 hours until it is ready. When is it ready? Well I like to make sure the feet clay is as close as possible in moisture content as the pot they will be fitted to. If they go to far you can always bring them back a bit with a water misting and plastic bag.
Wet clay is the least problematic to join and as it gets dryer then the risk rises. I like it to be dry to the touch but still quite flexible. That said I have used the same process successsfully with leather hard clay - all but dry and flexible only with high point pressure.

 At that point it can be handled with less risk of messing up the shape and it cuts cleanly without dragging. So this is when I make the final cuts up against the template. The clay also needs to be firm enough the be able to apply some pressure when making the join.

Then the foot is ready to join with the pot. I use a serrated rib to score the mating surfaces.

 Here you can see the scoring with a good crosshatching.

Apply slip to both surfaces. I like to use a long bristled artist's filbert brush; soft and flexible. For me slip is nothing more than a slurry of the clay body, which I keep in a screw top container always ready to use. Some recommend the use of 'magic water' (sodium silicate and soda ash active agents) which will flux the joint and that may be helpful the dryer the clay to be joined. The slip works fine for me but the critical step is the next one.

When you place the foot in place then rub it back and forth in position with downward pressure until the slip is forced out of the join and you feel resistance to further movement. At that point make the final adjustment in position with reduced downward pressure and it's set in place.

Apply some gentle finger pressure all around the joint line and then brush around the joint line with some more slip. A little further finger massaging and smoothing and it's nearly finished.

 My final step is usually a final brush with the filbert with straight water to remove any remaining excess slip and to finally moisten the joint.

Thursday, 11 April 2013

Post 87 Even kiln temperature

When I bought my secondhand kiln it came with a number of shelves and assorted props. The big shelf on the floor of the kiln was cracked - right across the middle. When I had the kiln delivered and gave everything a closer examination that crack in the shelf remained a mystery - it looked like a stress failure; if it had been dropped it would be in many more parts than two. This was the start of another discovery thread.

I'd read recommendations that you should have the first shelf on the floor of the kiln - why I'm not sure; perhaps to protect the more fragile insulating bricks. The shelf material is an amazing refractory material, really hard, really rigid and able to sustain high temperatures, often just supported only around the edge, without significant movement. But sitting on the floor of the kiln it would have seen quite a temperature differential between its upper and lower surfaces during firing. The upper surface would have tried to expand more than the lower and the shelf would have tried to bend, arching upwards, but being of a rigid material all it could do instead was to  crack.

Having come to that conclusion then, from the first time I fired the kiln, I set up a bottom shelf supported on stilts about 25mm off the floor. I had plenty so used about 12. Over a few firing cycles it seemed that the pots in the bottom of the kiln were not as completely fired as in the top. A gas or wood fired kiln sees the movement of the combustion gasses through the kiln and the forced convection of the draught exposes the work to a uniformity of heat work. In the unvented electric kiln which relies more on radiant heat at the higher temperatures, convection does however come into play and you can expect up to 25 degrees C differential in temperature from top to bottom. This can have quite an impact.

So I bought some pyrometric cones, tested and confirmed that this was indeed happening and it was a big difference, with the biggest step occurring right at the bottom of the kiln.
My first step to overcome this problem was to reduce the width of the shelves above the first one. You can see that in the picture below. This reduced the 'working shelf space' in the kiln but it made a big difference in even temperature. Perhaps with a tighter wall/ shelf clearance convection and radiation were impeded.

The last couple of times I've glaze fired I have raised the lower shelf even further, now to 100mm off the floor and more importantly above the height of the first heating element. This leaves some 'dead space' in the kiln but I'm getting a better result throughout the kiln. Perhaps the lower element can now play on that lower space to provide some underfloor heating to the bottom shelf that previously wasn't happening. If the shelf is hotter then the work on the shelf will be too.

Modern kilns which offer multiple heating zone controls would be a joy to operate, but if you haven't got that you have to see what happens and respond. Mine is just single zone control and the ability to preset the whole firing schedule and walk away is just so good. There is no substitute for vigilance however because particularly at the higher temperatures as the kiln elements age they may not deliver the ramp you are asking for. Because both time and temperature are so important, spending longer, at elevated temperatures, than you think, will have a big result on the cone firing result you get. I'm tracking the total elapsed time of my firing schedule, firing by firing, as a measure of element condition. The other valuable practice is to plot a graph of temperature vs time and compare this with the set schedule; very telling. At the moment once over 1100C the best rate of heating I can get out of mine is just a bit more than the 85C/hr I'm looking for, while at the lower temperatures 200C/hr is achieveable.
When I last fired the kiln as setup above I placed a single cone 6 cone on the second top shelf and another on the bottom shelf.

This is what they looked like after firing.

The one on the left, from the upper shelf ,has started to fall and the other from the bottom shelf was very close to completion. By my reconing I'd say I reached cone 5.95 on the upper one and 5.8 on the lower. After more than 3 hours at temperatures over 1000C the schedule was probably within 2 minutes of having the upper cone come to the horisontal. The very top shelf would no doubt have reached cone 6, so overall an excellent result, confirmed by the even fired appearance of the pots.
 As usual it's about a lot more than just making pots.

Monday, 1 April 2013

Post 86 New pots

In my latest firing I glazed a couple of my rectangular Sabani pots with brown toned glazes that came through my latest glaze tests. That was a firing I did in my little development kiln which works very nicely and  fitted 36 test tiles and a shohin pot.

The Sabani pots are about 360 x 250 x 78.
This first one, Pot 48 is based on a Post Tomato Red base, coloured with a mix of RIO and Yellow Ochre and has produced a nice deep and warm plum red brown. The development work was focused on developing glazes which would be suitable in colour and surface finish for conifers which are rarely seen in anything but unglazed pots made from a dark clay body. There are no commercial clay offerings here in Australia that replicate that body colour and so a glaze of the same tone meets the colour goal and at the same time provides a more durable clean surface. Glazing the feet completes the simulation.

This one, Pot 47,  is more of a bronze brown with some red highlights. It is based on my standard high calcium satin glaze but is principally a chrome brown (chrome plus zinc) with some RIO as well. It also is a good simulation of a different unglazed clay body, and also has the feet glazed.

The next two pots are a couple of Bekabunes at about  350 x 256 x 64.

The first one, Pot 46, is glazed in my Mint Green glaze and the next one ,Pot 49, in my new Buttermilk finish.

This firing also saw the last of a few prepared shonin pots.

The first ons is a hand made wire cut pot at about  190 x 145 x 55, glazed in a flat iron rich glaze. Quite a rustic finish.

 This one is a bowed wall rectangular pot about 175 x 130 x 50 in a breaking blue glaze.

And the last one is a similar pot in an offwhite/parchment glaze with heavier application around the lip.