Having carried out the carving, it is vital to retain the deadwood effect by treating the carved area, be it the hollowed part of the trunk or a jin (dead branch). This treatment will guarantee that the colouration of the deadwood is preserved as well as preventing insects and other pests from destroying the plant. The agent most commonly used to preserve and provide the greyish-white deadwood colour is lime sulphur.
Lime sulphur is a mixture of calcium polysulphides, often used in horticulture as a pest control agent. It is normally used as an aqueous solution which is reddish-yellow in colour and has a distinctive odour, that of rotten eggs. With bonsai, undiluted lime sulphur is painted onto exposed dead. This results in the wood being bleached, giving a pale grey-white colour which, when it is weathered, gives the deadwood a natural appearance. When applying the lime sulphur, it is important to confine it to the deadwood only; avoid painting it on other parts of the bonsai, notably the bark and foliage but also the pot containing the tree. It is best to cover the pot, the soil surface and where necessary, foliage-bearing branches with newspaper in order to protect those areas when applying lime sulphur. Care must be taken in its application as lime sulphur is very alkaline (pH of 11.5) and hence is corrosive to living things.
Lime sulphur suitably diluted, can be used as spray for deciduous trees for controlling bacteria, fungi and other insect pests. Recently, its’ use as a form of pest control is no longer recommended, so its’ sale and use is now essentially to bleach, sterilise and preserve deadwood on bonsai as well as providing an aged appearance. The principal source of lime sulphur would be through a specialised bonsai trader.