Post 64 Some pots from my collection

Another Christmas has come and gone and this will be the first for many years that I didn't score a new bonsai pot for a present. For a long time that has been my standard request for and ABC event ( aniversary, birthday, Christmas). At least I can't be accused of being boring anymore- well at least not for that reason.

The motivation for getting into making my own pots was about getting bigger and better for less. I didn't know a lot about pots before making them myself and I think many enthusiasts would be the same.

Most people at some point in their lives will have bought ceramic tiles, for a reno job, a new house or simply repairs. If you reflect on that purchase you might recall the information available about the different types and classes of tiles for different applications and what they may be exposed to.
 There is a clear distinction between non-vitreous, semi vitreous and vitreous tiles. This classifcation has much to do with the type of clay and the firing cycle it may have been matured to. You would chose between them depending on whether they were to be located inside or out, on the floor or the wall etc. There is a clear quality, service capability and price relationship at work with ceramic tiles and you get what you pay for.

Such a pity then that the same level of information is generally not available when purchasing bonsai pots, beacuse the same considerations should apply; what sort of clay was a pot made of, how was it fired and how will it perform in service.

This pot for example is a nice shaped little unglazed oval pot about 370mm long. Before taking the picture I gave it a vigorous wipe down with a damp cloth and then let it dry, no brushing. The pot has been out in the weather for years. It has provided good service but before even thinking about using it for a displayed tree some serious work would be needed. Actually now I wouldn't even think about it. It's just a grow pot and I'm just keeping it long enough until I have one of my own to take its place..

As you see there is a whitish deposit on the surface of the pot. This might be lime scale but I have others of a different origin which do not suffer from that so I am more inclined  to think it is efflorescence, the migration of slightly soluble salts from within the ceramic material to the surface; the sort of thing often seen on new brickwork. This is a reflection on the quality of the original clay body and what may have been added to it for various reasons. I suspect this is a low fired earthenware ceramic material which in tile terms is non or semi vitrified, which gives it a level of porosity that allows water to move through the pot wall and carry salts to the surface. That porosity also allows and supports unattractive biological patina to grow on the pot, futher diffusing the appearance and colour. Unfortunately in the absence of information about where it came from, how it was made and its qualities you don't know if the pots you buy will look like this one in a few years time.

I now know you can tell a low fired pot from a high fired pot by the bell test. Support the pot on a finger through a drainage hole and wrap the pot with a knuckle - to get anywhere from a thunk, to a ping to a resonant bell.  If you don't want a pot that looks like this one then if they don't ring like a bell don't buy them. A drop of moisture on the pot wall will also help you understand its porosity, a key influence on future appearance.
Knowing what I know now and having made and used pots in both earthenware and stoneware, I would never ever buy an earthenware pot again. If it wasn't stoneware I wouldn't touch it no matter what, I'd rather use a plastic pot.

Glazed pots are a different challenge to assess.
 

 This pot is a shohin sized glazed oval. It also is a few years old and has spent all that time out in the weather. When I bought it the glaze was a most attractive high gloss and you can see where it has run in the firing to give a gradation in colour under the rim. The picture is a truthful illustration of its current state. The glaze now looks like it's been sandblasted to remove the gloss leaving a very dull surface appearance. Once I just thought that a glazed ceramic surface was glasslike and forever. Now I understand the chemistry and that is only so under certain circumstances.

Most folks will at some time in their lives have been in a limestone cave - stalactites and stalagmites etc. They take a long time to get like that and have come about through dissolved limestone redepositing from drops of calcuim carbonite rich water evaporating and leaving the crystaline material behind. That's why the mites and tites sparkle. But of course how did the limestone dissolve in the first place. Well easy really; as rain falls carbon dioxide in the atmosphere dissolves in the rain, turing it into dilute soda water, otherwise known as carbonic acid. Dilute acid will also attack the surface of a glaze, if it is not correctly balanced and stable. Glazes which are used on ceramics for food service by professional suppliers will be formulated to be resistant to attack by dilute acidic food materials; it is possible and simple enough.

So back to the pot. The little blue / green pot glaze is what I call a showroom glaze; looks great in the showroom, but never ever take it out in the weather or it will wash off! Yes it really does start to wash off over time and it's the surface, the reason you bought the pot,  that goes first. I've got a few pots like this, how about you? This is a really difficult issues to deal with at purchase time. The only way to beat it is to know where your pot comes from and how it has been made.

If you are interested in how your unglazed and glazed pots will look after a few years out in the weather and your retail pot supplier offers no information about their pots other than price, then pretend you are buying ceramic tiles and ask more questions. This is why I now make my own but there was a time when I decided to go right up market; next time I'll show you my two Tokonome pots.

Post 63 Ceramic dovetail

We all know about timber dovetails, those traditional little reverse wedge shapes used to connect pieces of timber in a really strong joint. Dovetails in drawers continue to be the hallmark of a well built and valueable piece of furniture.

But what about stone or ceramic. I got thinking about this recently when a pot came out of a bisque firing with a crack in the side wall. This is only the second time this has happened and it is a bit annoying. After having invested the time and energy to get it here it would be disappointing to throw it away, but to continue to go to a glaze firing would amost certainly result in the crack opening up and rendering the pot almost un-usable. I've looked for but haven't found an approach on the net about how to repair it for a reasonable glaze firing result. If anyone has an answer I'd love to hear it.

I think I know how the crack happened and how to avoid it in future; a question of differential drying stresses.

 In this photo the crack is at about 7 oclock, just left of centre on the rim. Here is a closeup. It would be a nice pot and I was making it for a japanese box forest.

So how to fix it. There are well established practicesboth new and old for repairing broken ceramics, but none of those methods will survive the changes and temperature of firing to maturity. What ever you use has to contract 6 or 7% with the body of the pot, retain the pressure on the crack faces and not burn up at 1230C.

The ancients used metal  'clamps' and dowels to join masonry in the days before reliable cement / mortar technology. The Greeks used pieces of iron set in holes in the masonry around which molten lead was poured to secure the joint, as above.

This one is a double dovetail or bowtie from Egypt at the ancient temple of Dendera

This picture is of the Temple of Apollo at Delphi in Greece and on the foundation blocks you can see the interconnecting iron clamps - installed like staples to keep the blocks together. This was an early technology to earthquake proof a building.

 And for the students of history can anyone tell me what this picture is all about. Well in the chaos of the post Roman world when iron production went into disarray you had to get it wherever you could. So the ancient world's ruins became both stone quarry and iron mine, where it was sometimes easier (cheaper?)  to chisel through the stones in a wall and extract the iron clamp than source freshly produced material.

I do remember too, though could not find a picture, of the stonework on Fort Denison in Sydney Harbour. As I recall stone bowtie joiners were used there to tie together the monumental stonework on the wall of the big gun emplacements. Perhaps this was commonly used in 18th and early 19th C defensive military stonework. If anyone has got a picture of this please send it to me and I'll post it.

 Well all very interesting indeed and mostly well before the time of bonsai so not really relevant. I agree of course.  
But with all that perhaps there is some precedent for me to fix my pot with a bowtie double dovetail clamp made of the same material as the pot.

So on the inside of the pot I've placed a bowtie that is about 2/3s of the wall depth and also drilled a small hole at the limit of the crack to stop propagation. Bisqued clay is nicely workable. Before firing I'll sprinkle a little galze in the base of the bowtie recess and around the join to secure it in position, then glaze right over the top both inside and outside. The crack may still be apparent, but after reaching maturity it will be totally stable and with luck the wall will now not gap open. Time will tell.

That's as far as I've got on this one and will now have to wait for the next firing opportunity. Speaking of production disarray I'm doing a few little renovations in my workshop at the moment and both pot making and firing is in total disarray!

This will likely be my last post for 2012. Season's greetings to one and all.

Post 62 A branch hidden may be a branch wasted

I have mentioned previously the value I get out of having one of my trees in the house on rotation. Each one gets a turn for a week and I get to look at it every time I go backwards and forwards. It is always hard to find the flaws in your own trees, but then quite surprising some times what you can see when there is only one to look at.

This willowleaf ficus (Nerifolia) has been styled with a well defined branch structure which is a little different from the umbrella canopy style you often see it in. The second branch connects to the trunk on the back of the trunk. Up until now it has been oriented to be pretty much in a sight line directly in line with the trunk, away from the viewer. The foliage pad can be seen and is arranged to provide the background depth to the tree. The prominent space between the left hand branches is too prominent. So why not fill the space and at the same time get some value out of that second rearward facing branch.

The next picture shows the temporary restraint in place to set the branch in a new position. This fills the space a little, provides some visibility of the branch and retains the background foliage pad for depth.

Courtesy of a little photoshopping I can take out the restrainer to more clearly see the final result. It will be a matter of viewing height but a possible problem this creates is the close alignment of the rear branch with the first right-hand branch. This can be resloved at a later stage with a little 'S' bend in the rear branch to lower the visible part by about 10mm to get a result.

I like the way taking a picture of a tree  and thus compressing it into two dimensions sometimes makes it easier to take a uncompromising clinical view about styling You get to see it in a different way. A photo shop like tool is also a good way to move branches around and experiment before you take irreversable steps.