Water has a profound effect on wood. When moisture content increases. wood swells up. And when moisture content decreases, wood shrinks.
When moisture content changes too much, joints can open up, the wood can bend, and it can split. And long slim pieces of wood such as jian and dao blades, are particularly prone to movement.
In order to minimise these effects, wood must be kept at an ideal humidity.
|The drying room with jobs in progress|
The recommended relative humidity for houses is 50%, with a recommended minimum of 40% and a maximum of 60%.
Some musical instrument manufactures are even stricter, and recommend that humidity should be between 45% and 55%.
To ensure that Tigersden jian and dao have optimum stability, the wood is first stored in the drying room until the moisture content has equalised. The wood is then worked in stages, and is allowed to rest in the drying room in between those stages. The above picture shows a number of jobs in progress, from sawn wood, to almost completed jian.
This extra resting time extends completion dates, but the waiting is well worth it for that extra stability.
|Stored in an ideal humidity of just under 50%|
Humidity and moisture content are just as important for the Martial artist. Mudao and Mujian stored in very damp or dry conditions will be prone to warping or splitting.
Most houses will fall within the recommended humidity, but care should also be taken to keep mudao and mujian away from heat sources, including radiators and strong sunshine. Modern houses with central heating and no humidifier, have been responsible for causing irreparable damage to wooden furniture.
|Shrinkage crack in oak furniture panel|
When wood is exposed to very dry conditions, it can distort or split, and in extreme cases, shrinkage can become permanent. The picture above shows a wide shrinkage crack in a 1930s oak, desk panel. The split was caused by central heating, but even though it is now the correct humidity, the wood will no longer return to it's original size.
|Some of precious woods in the drying room|
The last pic is an enlargement of some of the exotic woods in the drying room. These come supplied with the ends sealed in wax to reduce the effects of humidity. Some of them are completely encased in wax. Similarly, oil finishes, and lacquers help to protect against moisture changes.
Wood is a living material, and when treated well, wooden objects last hundreds, and in some cases thousands, of years.