When preparing for teaching assignments a few trees needed for display are readied, foliage and trunk/s are cleaned as are the ceramic pots and any unwanted residue (alkaline scale) is removed. It is the same practice one would undertake if exhibiting bonsai at a show, because presentation is everything students can see the real tree/s in person, which has more impact as opposed to on-screen pictures.
Inspecting the pots containing trees, one a blue rectangular pot made in Japan when picked up simply fell apart, the damage is severe and yes it could be repaired using a two part slow curing epoxy resin, which according to the manufacturers (Loctite) has “special formulated materials that are great to bond and repair plastic, metal and concrete or surfaces exposed to water.” But how does epoxy resin fare when exposed to extreme temperature differences that is the question. If this pot were to be repaired it could only be used for plants from temperate zones often referred to as ‘indoor bonsai’, that can survive quite happily out side in the summer months, but not during the winter as the chances are the pot may not survive.
Another pot subjected to winter conditions had three hair-line cracks, hence the tree was removed and replanted in another container and the cracked pot was cleaned, on further inspection the three cracks ran from the rim down into the middle of the pot’s base both on the outside and inside of the pot. This blue green glazed ceramic pot is/was not expensive by any means, it is a cheap Chinese pot mass produced as one can tell from the pot’s rough underside. But what is attractive about it is the shape – a feminine shallow oval befitting an informal upright (Moyogi) or literati (Bungin) style and for this reason alone it was decided to ascertain if it could be saved.
Using a Dremel with a fine cutting wheel the cracks were gouged out halfway into the pot’s surface on the inside and the base only, the ceramic outside was not touched because it would have ruined the overall appearance. The glue used for the repair was the same as used for the Japanese pot (slow curing two-part epoxy resin Loctite 60 min) and for the moment it seems to have solved the problem. The pot and can still be used, but it is doubtful that it can withstand another winter moreover, neither of them can be used for public display.
To answer the question of why the cracks appeared some detective work is required, being a mass produced pot from a mould where the clay is forced in, dried then fired is a relatively cheap and cost effective way of mass production. But if the clay has not been properly formed, bonding defects within the structure go undetected. The clay has to be worked and kneaded many times to make it malleable and durable before it as ready to be formed into its intended shape. Many years ago before the advent of technological automation, clay preparation or kneading was done by highly skilled people who knew instinctively when the clay was ready, which was then given to the potter.
Mass produced pots or containers sadly lack the required amount of kneading whereas, with hand-made pots this crucial stage of preparation is completed. The firing process is also a critical factor, in China the average temperature is approximately 1260 degrees C and the fired ware is referred to as ‘biscuit’, in Japan firing temperatures are higher 1305 to 1800℃, but much depends on what type of ceramics are being made hence, temperatures are adjusted.
In the case of the repaired Chinese pot, the overall structure has gradually weakened through time due to the elements and because it houses a tree, the soil medium is always moist. When the weather turns cold the moisture particles begin to freeze and expand causing hair-line cracks to form. Did this problem (a) originate when the clay was being formed – Kneaded (b) is it due to the onslaught of winter conditions or (c); the degradation of the clay’s properties over time, arguably it is all of these factors.
Generally speaking Chinese mass produced pots are relatively inexpensive but their hand made are not, Japanese mass produced pots are slightly dearer and of better quality and their hand made pots have a higher retail value. Hand made pots designed by individual artists can command very high prices as their work is of high quality and usually made to order for example, a Tokoname made bowl size: approx. 48 x 48 x 10 cm by the Japanese artist Reiko will lighten your bank balance by 625€.
However, this is not to say that the more expensive pots are not infallible, because they are; quite a few pots which have been in our possession since the 1970s and are of good quality have succumbed to the ravages of winter. Perhaps the question is; do quality bonsai pots have a life-time guarantee? – probably not. Until next time BW, Nik.
N.B. If you are interested is seeing how a hand-made rectangular pot is constructed, here is a suggested link: