Wednesday, 23 July 2014

Post 159 Reglazing a pot

I glazed Pot 105 back in February using a glaze which was less than successful. It was one of those things that looked interesting on the test tile but didn't live up to the promise on a pot.

As glazed in February

This is what it looked like at the time. That got me looking into reglazing. I've seen discussion and tips about how to do this from time to time but never had to confront the challenges.
A bisqued pot is entirely a different proposition to glaze compared to a glaze fired and vitrified one. The beauty of the bisque is its porosity and capacity to suck the water out of the glaze mix as it is applied, leaving the paste to quickly dry to powder which adheres to the surface.

A glaze fired pot has no absorbancy at all and so applying the glaze slurry is an entirely different proposition. Various surface treatments are sometimes mentioned to provide a way for the glaze to attach to the surface. Abrading the surface sounded like far too much work and the alternative of hair spray or the like was not the next best option for me.
The idea that sounded workable was to preheat the pot; the suggested mechanism being that the heat would evaporate the water in the glaze mix to simulate the absorbancy of the bisque.

After reglazing with a red/brown glaze, two coats.

The pot is a bowed wall rectangular pot. This shape is far more reliable in firing than a straight walled rectangular pot, coping better with the movement during vitrification, with less evident distortion. In use it is a very attractive shape too, not as soft as the oval and not as rigid as the rectangular, a useful middle ground.

So that's what I did; heated the pot in the kitchen oven to about 70c to 80c and then painted on the glaze. I went over the pot with two coats of a red brown glaze and reheated again before the second coat. Once done the glaze did not look at all fragile on the surface and none of it dislodged with movement, which I was concerned it might.
I'm much happier with the result this time around and now have a technique in my toolbox to use for the next glaze departure from plan.

Tuesday, 22 July 2014

Post 158 Hairpin Insertion graft update #2

In March I posted an update to my Hairpin Insertion graft on the Queensland Small Leafed Fig.
Since that time they've grown on nicely and I have just separated the scion host plant from the second graft.

In the above picture you can see both grafted branches. The swelling at the branch/trunk union is typical of any branch and the 'seam' at the join will dissipate over time. The 'inward' stubs have been left in place for the moment. I'm interested to see what happens with them.

Panning out a little you get a better view of their positioning.

And then at this range you can see the spaces in the tree structure that the branches are designed to fill.

The whole process would have been and could be much shorter if I'd drilled further into the trunk at the start. Around February the hairpins worked their way out as they put on weight so I redrilled deeper, reinserted and used a small 'keeper' in the elbow of the joint to allow the wire to hold it in position. Since that time it has progressed very quickly. The hole depth needs to be 3 or 4 times the width of the hairpin bend. The calus formed by the wound guarantees a good joint.
I'm very happy to see that the new branches are filling out in diameter and it is great to have them in the right conformation on the trunk. The tree is still growing despite our winter conditions. As the weather warms I'll prune the new branches to promote branching and then select a secondry on each to extend and fill out the girth again.

This graft technique was inspired out of dis-satisfaction with thread grafting and approach grafting for branch development. It has proven to be a simple, effective and quite foolproof process delivering a great result; a branch that looks like its always been there.

Thursday, 17 July 2014

Post 157 Winter and the dark side of the moon.

I was away at the time but I'm told that winter started here around the end of July when the daily max dropped under 20 and everyone rushed to close the windows and put on something warm. Since then it's got really cold, seriously it has. Just last weekend it was 4C in the morning, that's about the coldest I can remember. And there was frost in the low lying areas. How does that work frost at 4C.

Well yes I looked it up and apparently it's all about radiant heat dissipation and the universe's pursuit of equilibrium. Sounds profound but like so much it's just magical science and nothing supernatural. On a clear night the relatively warm ground radiates it energy in an effort to reach equilibrium with the close to absolute zero temperature (-273C) of deep space. The air in between isn't much of a barrier and so even with small above zero air temperature the ground can go sub zero causing moisture condensation and freezing.

This would suggest that the ground temperature falls below the air temperature all year and perhaps that is true too. Even at warmer times of the year I've noticed a similar thing happens with dew forming on the grass at dusk and on the metal roof of my house. At dusk as the day cools and the sky darkens the relative humidity of the air can reach saturation. At the same time the radiant heat transfer of the metal roof chills it to below the ambient air temperature and so condensation forms. But interestingly it forms in patterns and those patterns correspond to the areas where the insulation is in direct contact with the sheeting. Where the sheets are secured to the roof structural battens and so exposed to more warm thermal mass the condensation doesn't form.

Energy production comes out of temperature differentials but I guess something like 4 or 5 degrees C might be just too little to be useful. Still it could probably drive an IPO.
The thing I don't understand is why this dusk ground condensation does not form on the ground where there is a roof or covering structure but otherwise open to the air. It's like there is a perpendicular line from the edge of any overhang and the dew does not form on the overhang side of the line. But then you don't have to understand it to use it. I'm trying to maintain the condition of a couple of my evergreen trees at the moment for a show and in the absence of a heated plant house all I can do is put a cover over them at night and save them from a couple of degrees of cool.
For a sub-tropical/temperate area we can get a lot of rain in the year but it usually falls in summer storms and our winters are dry. Warm dry winters make for parched dry landscapes and that's our lot at the moment. The gardeners amongst us are working hard to keep plants alive.

The one thing the chill has been good for is the colour of some of our deciduous bonsai. I have a couple of what I think are malus trees, one a cutting from the other. It is remiss of me but I have no record of the exact species/variety. I've not seen flowers or fruit on them, perhaps they need more chill for that than we can offer. They certainly develop some mean thorns but right now they have coloured up to a beautiful claret colour and the longer the cool goes on the leaves go to a pink red.


Meanwhile the Celtis turn a beautiful clear lemon yellow. The next picture is from one of my yamadori stumps.

I've let them grow this year and so they look pretty untidy but the colour is great and if I can ever tame them they will make a great show.

And just to finish up with the dark side of the moon. It shows just how powerful radiant transfer to the wider universe can be. While the side facing the sun can run to 120C without any atmospheric insulation, the dark side can drop to minus 150C. Dusk must be a pretty interesting time on the moon. No complaints from me about frost at 4 degrees!