Tuesday, 30 July 2013

Post 112 Celtis Sinensis

I've been jealoousy reading recently about folks in southern states going on digging trips to collect all manner of bonsai desirable feral trees. That got me thinking about what we have here in SE Qld and the obvious answer is Celtis. Celtis Sinensis make fantastic bonsai here; they grow quickly, ramify well and the leaves will reduce down to a very small size. Just search for 'celtis bonsai' to see the standard achievable.

With our climate, some potted celtis will go through the deciduous cycle, producing a beautiful lemon yellow colour in the autumn. It is very unusual to see a celtis growing in the ground do so. They will do no more than take a short growing pause for winter.

The problem is that they like it here too much and have now been declared an environmental weed, despite the fact that in many parks and gardens there are some very fine mature landscape examples flourishing. The rules for environmental weeds are that they not be bought or sold. The seeds, spread by birds, germinate well in creek catchment and low lying damp areas, where they can crowd out the local flora.

As I've driven around the bayside lately I've been looking for the feral ones and have been surprised at just how many there are. In one place  I noticed a couple growing up through the long grass on a footpath. The area had obviously had some maintenance a couple of years ago and these two celtis had been cut off close to the ground.
What could I do but my community duty in removing these dangerous invaders from the natural environment. So that's what I did, roots and all, and brought them home to start a new life where they will cause nothing but delight.
These two trees are in the first two shots following. You can see the cut off stumps and also the new growth going over the top of the cuts.

The first one was growing on a small sloped bank and so has a nice bit of movement already in the quite heavy trunk.

The second one has produced multiple regrowths - plenty to chose from once it recovers. I've put these two in poly boxes to grow on. This one is a natural for a forest group.
This recovery capacity demonstrates the value in having a two stage collection process. Stage one is to cut the top off in situ and make the most of a strong root structure to drive vegetative recovery and then come along some time (2 years perhaps) later and disturb the roots; if they are still there!

I had found another site nearby that was weed heaven, full of celtis, ochna, lantana and asparagus vine; just amazing. There were two that I decided to take out entirely and many more that I just cut the top off for 'later'. The collected ones are back home now planted in the ground ready for spring.

This one was a twin with the main tree about 6m tall and trunk at the cut about 100mm in diameter.

The second was a fused clump, obviously a group of seeds in one bird dropping, with 5 trunks, and an elongated 'footprint'.

Both of these were growing in damp soil in an area prone to a bit of acid sulphate conditions and so the trees confined themselves to mostly surface roots. This made them comparatively easy to dig out and fostered the development of nice nebari already. All the trees I dug had good fibrous roots near the trunk and so have a good chance of recovery. I'm looking forward to seeing some shoots pretty soon.

Thursday, 25 July 2013

Post 111 Tanuki No 4

After seeing all the Junipers in the deserts and mountains of the SW USA I have been inspired to make Tanuki no 4. I was particularly taken with the growth habit where the trunk and or branches have a ribbon like or ovoid cross-section, often with the live vein growing along the edge. So that was the inspiration for this tanuki. I also tried to bring in a feature of the trunk splitting at the base. It is in offwhite stoneware and fully fired, finishing up at about 330mm high.

This is what I think will be the front. Even though the apex bends to the rear it will be the live tree that comes through that final loop towards the front.

Left hand side.


Right hand side

I have some air layers underway on a Sargent Juniper which will be ideal for installation on the tanuki. The branches I'm layering are long and straight, long enough for the bends and twists to get to the top and flexible enough too; just perfect. I hope by late summer to be able to get on with getting them together.

Monday, 22 July 2013

Post 110 Why annealed copper wire?

Just before we get onto that I found a better illustration of what happens when we bend wire - illustrated on a stress strain curve.

We start by winding the wire onto the bonsai branch. Depending on the winding pitch and the size of the branch etc some parts of the wire will still be in the elastic range and some parts may have been bent far enough to reach the plastic range.

As we start to reposition/reshape the branch by bending it and the wire we take the wire into the plastic range between A and B. If you drop a vertical line down to the Strain axis that will show the distance moved.

As we continue to bend in the plastic range more effort is required because the wire hardens with the work being applied - it work hardens.

If we keep bending to C and then release the pressure, because we are no longer in the elastic range the wire does not retrace its path but follows the line down to F. So going to C meant that we bend the branch a distance of G and then when we take off the pressure it returns to F. That is without any consideration of the additional recovery forces applied by the branch which remains elastic, and wants to go back to where it started
That's why when you use wire to bend a branch of any maturity you ALWAYS have to bend it further than you want to reach a certain position.

That analysis is based on the generic ductile metal curve. It gets really interesting when you start to look at the curves of the real data for Drawn Copper, Annealed Copper and Aluminium.

Annealing of copper is done to change its properties to become softer and more maleable, by heating to a high temperature and then cooling to change the crystalline structure of the material.

Thanks to Cambridge Uni for this chart.

The RED line is for Work Hardened copper - and with wire being made by a die drawn process it will be work hardened.
The BLUE line is for annealed copper.
The PURPLE line is for pure aluminium.

 So what does this tell us?

You can see that the work hardened copper has a short elastic displacement but with high effort. This says that relatively it takes much more effort to change its shape and unless you take it far enough it will come straight back. Once it yields however it doesn't work harden much and will continue to deform with reducing effort.

It gets more interesting when you look at the annealed copper curve. It basically has no elastic range, is easier to bend, deforms straight away and the more you bend it the harder it gets, all good characteristics for bonsai work and exactly why some would say that if it's not annealed it's not worth using. To put some cream on the cake the fact that it has no elastic behaviour means it is more likely to hold its position when load is released.

Now the aluminium. It has a short elastic range and then after that is like the annealed copper only easier to bend (and thus has less holding strength). But you can only take it so far before it will weaken and break. This data also shows that the peak stress of aluminium is about half that of annealed copper. In the numbers I was using in the last post I assumed it was 70% higher. If it is 100% higher you are going to have to use an aluminium wire of around 20% increase in diameter to match the annealed copper, so it's not such a big difference, but you still have the overbending/recovery to deal with.

 So today's conclusion are:
  • Annealed copper is much much better than aluminium, in all regards.
  • If you are going to use copper if it's not annealed you might be better off with aluminium.
  • If you are going to use aluminium use a heavier wire than you would for copper and be prepared to have to overbend to get a branch to stay where you want it.
 Isn't it great when the science confirms what you already know.

Saturday, 20 July 2013

Post 109 The science of wire

When we wire a tree branch to bend and hold it in a new position, we want the bending resistance of the branch to be overcome by the willingness of the wire to take a permanent deformation; but what does the science tell us so that we can improve our chances of success. We all know from our own experiences and from watching others that wiring is far from a simple proposition.

When you bend a piece of wire a little bit it will elastically come back to where you started. Bend it some more and you can eventually feel it yield, come back a little and then stay in a  new position. Now try to bend it back and it requires more effort to do so than the original bend. All metalic materials behave this way but each in different quantities some requiring more effort than others for example to get to yield.

Mechanical material science tells us that materials have a measurable property called the Modulus of Elasticity which defines how that material behaves when a bending force is applied. This Modulus is the slope of the stress/strain curve. For stress think force and for strain think displacement or distance.

This is what a typical curve looks like. The bending starts at the intersection of the axes. As the stress is increased the strain does also etc.

The elastic region is where you bend and it comes right back. In this region a stiffer material like copper will have a steeper angle than for a softer material like aluminium, which says that for the same force the stiffer material will bend a smaller distance before reaching yield.
Yield is where it begins to take on a permanent new set.

We know that from experience but it's all in the curve. The slope of this region is the Modulus of Elasticity and measurements tell us that Copper's modulus is about 1.7 times that of Aluminium.
So for a Copper wire and an Aluminium wire of the same diameter the Copper one needs 1.7 times the effort to bend the wire the same distance as the Aluminium one. Or more importantly for bonsai the Aluminium wire will bend 1.7 times as much as the Copper BEFORE reaching yield, which is where we need to get to bend the branch. That's a pretty important factor if you are looking for fine changes in ramification.

What else does the curve tell us.  Once we pass the Yield Point we get to the Plastic Region where the long term shape is plastically changed; but it's not as clearcut as that.

One of the other dominant wiring observations and challenges is that when you bend the wired branch, even after reaching the end of the purely elastic region, when you release the pressure there is certain amount of recovery in position. That is to get to a position you have to bend it further than you want to compensate for this recovery. The two reasons for this are that the wire characteristics retain a level of elasticity applying from the new point and under the counter pressure from the branch which is still in its elastic range the wire is bent back  towards its starting position.

On the following graph we track along the red line to Yield, a little further and then release the pressure. As the pressure comes back the displacement (Strain) tracks down the short line to X which will be the starting point for any subsequent bend. This shows how there can be some recovery in the old position which is also exacerbated by the elasticity of the branch.

Having to bend further than you want to achieve wire yield and overcome the branch elastic recovery is when most branch fractures occur. The answer of course is heavier wire, but there comes a point where applying heavy wire, bending it and the branch and then getting it off eventually may be a few too many risks to the branch.

The size of the wire is interesting. It is self evident that heavier wire requires more effort to bend than lighter, but how much?  The cross-sectional shape of a piece of wire is circular and we know that the area of a circle is Pi * Diameter squared / 4 so if we double the diameter of a piece of wire its cross-sectional area is 4 times greater. The interesting thing about bending however is that Bending Effort is proportional to both the Elastic Modulus by the Area Moment of the material shape. For a circle that Area Moment is proportional to the diameter to the 4th power. So double the diameter and the Bending Effort is actually 2 to the power of 4 greater, ie 2*2*2*2 which is 16 times greater.

So double the wire diameter and this needs, and you thus apply to the branch, 16 times the effort or force. That's the power of scale and why just small increases in wire size are so effective.

Now to compare Aluminium and Copper if we use a copper wire twice the diameter of an aluminium one it requires 16 *1.7 or about 27 times the effort to move it the same distance and by the same deduction applies that level of resistance to the branch elastic recovery!!!! And what size of Aluminium wire would you need to apply the same force as a piece of Copper wire? Well the answer will be the fourth root of 1.7, which is about 1.15 which says that an Aluminium wire just 15% larger diameter than a Copper wire will offer the same bending resistance. One thing that doesn't change however is the Modulus, the slope of the curve, which means that you still have to bend the Aluminium wire, even the bigger piece, further to get the same effect.

We need to think about the branch in somewhat the same way. A branch of more than a couple of seasons age will have its own elastic bending characteristic, recovering from a bend if you only go so far and then if you go too far as well all know you will reach yield. Unfortunately the yield we are talking about is failure, because timber generally does not have a plastic region. When we wire a branch and hope to achieve a new shape we need to exert sufficient force to achieve both the yielding of the wire and to overcome the elastic recovery of the branch. Unfortunatley I've seen too many demonstrations where branches are put at risk from over bending where the wire will never hold the position sought because of the characteristic of elasticity in the plastic recovery and insufficient wire weight.

 Now let's take a moment and talk about springs, actually to be specific Helical Springs, things like these.

The reason we need to think about these is that when we wire a branch we actually end up with a wound spring on the branch. So how do springs stay springy? Well because of the spiral nature of their design and the true length of the wire used to make them they enable the material to stay in its elastic region with a large displacement. This is true axially, because that is where they are normally deisgned to bear load from, but also laterally too, ie from the side.
Now the best way to be clear about that is to take it to the extreme of a 'slinky'.

This helical spring structure has no resistance at all to lateral forces with so many tight windings that the material will never approach yield. Let's define spring Pitch as the distance between any two consecutive windings. So with a slinky the pitch is the width of the wire and for the other springs above it is closer to half the diameter of the spring.

The issue of resistance to lateral forces is very important for our bonsai application because that is exactly what we rely on to hold the position of a wired bonsai branch. So what pitch should we apply when wiring a branch. Clearly a closely wound wire with small pitch will offer little resistance to the branch and the wire will be less likely to reach yield, ie useless. A very long pitch with only a couple of windings will give the best bending result but with little branch contact the wire may be ineffictive at containing the branch. The middle ground is best with as long a pitch as possible while still wrapping the branch.

A really interesting question after all this then is to ask if you don't have heavy enough wire to do the job what is the best way to proceed.

One approach is to double up with the wire you have. Ok so what do the numbers say about that. If one piece of wire applies a load of F then two will apply 2F.
Now two pieces of wire of diameter d would be equivalent to one piece of wire of diameter 1.4d, cross sectional area wise. We know from the bending stress calculation that the bending stress of the larger piece of wire would be the increase in diameter to the 4th power, or about 3.8 times ie 3.8F. So if you are going to use strands of the same wire you need to use almost 4 strands, not two, to get the same effect from one piece of wire of the combined weight of two strands of the smaller wire.
Heavier wire is always the best answer, more of the same will rearely do it and heavier wire, kilo for kilo gives you much better bang for your buck.

There is another approach and that is the one often used in extreme bending practise where straight sections of wire are raffiaed to the branch and then followed by a helical winding. This can work just as well without the raffia and as the straight sections are bent they will offer much greater impact than the same number of additional helical windings.

The other option is to use a branch bending clamp. I like these because you only have to bend a branch to the position you want and no further to provide for any recovery. You can also do it in a slow and progressive manner and get the bend exactly where you want it. Alternatively guy wires offer the same benefit when an appropriate anchor point can be provided. For a simple big bend I would much prefer the control and limited bending requirement of a clamp or guy wire in preference to the uncertainties of heavy wired freehand branch bending.

 The summary of all that is as follows; the Happy rules of wiring!
  • Heavier wire is many times more effective than its equivalent weight in smaller strands and with wire sold by weight the heavier wire will give the best bang for your buck.
  • If you have to bend a branch past the point you want it to stay your wire is not the right weight for the job.
  • If you need but don't have heavy enough wire better to apply straight strands along the branch under one helical application than additional helical bands.
  • When wiring apply with the longest pitch possible while containing the branch.
  • Stiffer wire is always better but the increase in stiffness can be countered by only a very small increase in diameter of the softer alternative.
  • If simple bends can be accomplished with bending clamps or guy wires, these will most likely offer controllable alternatives to getting a branch in the position you want.

Monday, 15 July 2013

Post 108 Three more new rustic Shohins

In the recent firing I also had another three rustic Shohins. I'm working on getting a few more of these in stock to take to a club visit I have scheduled for August. There seems to be more spontaneous purchase interest in smaller rather than larger pots. If people are interested better to have something for them which is not a big decision.

They are all around 190 to 195mm long and 45 to 50mm high. The first one is in a Custer potash / nickel breaking cream and the other two in the same glaze I used on the big moon/rock pot, using my standard base. The latter two have been textured with a piece of an old bandsaw blade - leaves a nice line either up and down or on the angle.

They would all go well with Aussie natives that have a light coloured trunk.

Saturday, 13 July 2013

Post 107 Big Moon Rock pot

I'm not a big fan of 'moon' rocks as you can probably tell from my normal pot styling. But then sometimes you just have to yield to persuasive efforts and give it your best shot.

This type of pot demands a certain type of tree. It has been made for a left leaning juniper that has all the appearance of having grown out of a sloping rock wall on the side of a canyon somewhere. If we can get some front to back and left to right slope in the potting medium, some moss and a few loose rocks, that will go along way to pulling off the simulation.

And so Pot No 68 was hatched. I built  it up with multiple layers of overlapping sheets of clay, upside down on a ball shaped form and then when it was dry enough to invert, pushed it around a bit and applied a little texture.

The pot is about 300mm at the highest point, 420mm long and 290 wide, just a strange shaped oval really, sitting on 4 feet and glazed. Here are some pictures from all sides and a detail to show the texture. I was concerned the glaze would fill up the fine textural detail but a light coat hasn't done that while contributing to a level of colour differentiation. The glaze should help keep it clean out in the elements where all those nooks and crannies will be nice homes for stuff to grow.

I'm happy with the execution but still not sure I'm ready to sign up to the movement and put one of my trees in one!


Thursday, 11 July 2013

Post 106 New 'Lava' rock pot

A while ago I posted a shot of Pot 52 with a highly textured surface reminicient of extruded lava. I was surprised at the response to it, no doubt by the many keen growers of australian natives looking for a pot to match some of the raw and textured bark of our trees.

I've been testing other ways to get texture into pots and have only just come back to the 'lava' wall with Pot 80. Here it is just made and still very wet. It's a round semi cascade pot about 300mm diameter.

And here's a closeup. Glaze will be a flat red brown, a little darker than Pot 52, in a few weeks time.

Wednesday, 10 July 2013

Post 105 Pot 69 in service

A couple of posts ago I showed Pot 69 fresh out of the kiln. It was commissioned for a nice little corky bark elm and here it is all set for the start of a new growing season.

At this point it looks like a harmonious match and will be even better when the tree is in leaf.

That's a nice tree and a sweet little pot even if I do say so myself.
It certainly looks so much better with a tree in it than sitting there empty. Could that be beacuse it's now a happier pot with something useful to do; fulfilled?
I would certainly be a happy potter to have it in my own collection, as I am to see someone else get the same pleasure.

Friday, 5 July 2013

Post 104 Clay shrinkage and deformation test

While my regular RHG has been missing in action I've used a couple of different clays to test them out. Some of the pots I've made from them have been in recent posts. Those pots are still drying and not yet bisqued.

But with the last glaze firing I fired a couple of test pieces of the Walkers Special and the Toast clay; as I have used in the past my now standard shrinkage and deformation tests.

 This picture shows the Walkers in the front and the Toast behind. The Walkers deformation is very similar to that I've seen with RGH under the same firing schedule - my cone 6 schedule. Toast moved far less, no doubt because of the heaving grogging of the body, which will elevate the maturity temperature of the clay and thus see less vitrification. The shrinkage testing pretty much confirms this suggestion.

In the shrinkage test I start with a bar of clay and make two marks exactly 100mm apart. Measure again when dry and after final firing. The Walkers shrinkage is 12% and the Toast 9% after glaze firing. RGH under the same schedule shows about 12.5%. The Walkers fired to a nice off white colour.

The big oval I made with the Walkers Special is nearly dry enough to leave uncovered after two weeks under plastic. I mixed in a little more RIO to buff up the final fired colour. It would otherwise be just offwhite.
Here's a picture of it the right way up. You can see the props under the pot that I use to support it while drying, separated from the pot by a piece of newspaper. The same props go through bisque firing with the pot and then are ready to do the same job in glaze firing. The Walkers clay has an amazingly smooth finish almost like it's been burnished. Now there's an interesting test to run some time.

The pot started when wet at 670mm and should now be down to 636mm; to get to 590mm when glazed; just right, if my shrinkage testing is replicated.