Bonsai (Japanese:  literally “potted plant”) is the art of miniaturization of trees by growing them in containers. Cultivation includes techniques for shaping, watering, and repotting in various styles of containers.Originating in China during the Han Dynasty, ‘bonsai’ is a Japanese pronunciation of the Chinese word penzai  The word bonsai has been used in the West as an umbrella term for all miniature trees.

Often bonsai gardeners wish to provide an aged look to the bonsai tree. There are several ways in which this is done. One of the most popular ways in which this is done are deadwood techniques. Usually, deadwood techniques are done on conifers. Deciduous trees tend to shed the branch, and heal over the wound. Deadwood techniques are often used to hide defects, such as an overlarge branch, or to reduce the height of a tree that is too tall. The wood is treated with combination of lime and sulfur, which is available from many bonsai outlets. This preserves the wood.

A Dwarf Japanese Juniper (Juniperus procumbens 'Nana') bonsai on display. Multiple deadwood styles have been used on this tree.

Jin

Jin is a bonsai deadwood technique. A Jin is meant to show age, or show that the tree has had a struggle to survive. Jin is either a dead leader at the top of the tree, or a dead branch. Jins in nature are created when wind, lightning, or the weight of snow breaks a branch. Trees with two leaders look unnatural, many bonsai gardeners turn the higher growing leader into a jin. This effect makes the tree look like it has been hit by lightning, adding to the feeling of age.

Uro

Jin are common on coniferous species of bonsai. However, Jins do not work on deciduous and broadleaf species. On these species, the dead branches just rot and fall off the tree. Instead, bonsai gardeners make small indents where a branch used to be, and new wood grows around it forming a small hollow. This is what bonsai gardeners replicate with Uro.

When removing a branch from a deciduous or broadleaf species, gardeners often make Uro. The cut that was made will not heal for 5-10 years. To avoid having an ugly wound for a decade, the gardener would make a small wound (usually with a drill) in an irregular shape, then treated with a lime-sulfur mixture. The lime sulfur mixture is usually combined with a small amount of paint a similar color to the tree to make it look more natural. If the paint was not included, the lime-sulfur solution would make it bone white.

http://en.wikipedia.org/wiki/Deadwood_bonsai_techniques