An Overview of Kauri Resin

The kauri copal which is used in varnish making is a fossil resin found in New Zealand. The resin comes from the kauri pine, a slow growing tree that lives to be about 500 years old and attains great size. The tree in appearance is not like our pine trees because it has leaves instead of needles. The leaves are from 1½\" to 2½\" long, from ½\" to ¾\" wide, and are of a thick, leathery, shining, greenish-brown color.

The kauri pine tree bears cones, however, which show that the tree is a Gynnosperm and is related to the pines. There are living kauri pine trees growing in the gum region at present which exude a soft resin. The fresh gum is said to be of no value to the varnish maker. The fossil kauri resin is dug from the ground at depths usually varying from 3 to 10 feet. No one knows how the fossil gum came to be buried several feet in the ground on a level where a former forest of kauri pine trees once stood.

It is known that gum exudes from kauri trees around wounds from broken limbs or other injuries. Fire probably destroyed the original forests leaving gum from the trees which winds and decaying vegetation finally covered over with earth to a new level. Thousands of workers, called gum diggers, dig the fossil kauri resin out of the ground. They use sharp metal spears to prod or drive into the ground in search for something hard.

Digging starts whenever any obstruction, which the spear runs against, is thought to be a chunk of resin. Excavations are sometimes made with machinery by companies that hunt for gum on a large scale. Water is also used in connection with machine digging in order to wash away loose dirt and to clean the chunks of gum. Kauri resin is found on the market in several grades, which are called pale kauri, brown kauri, and bush kauri. The pale kauri is the best grade and is a true fossil resin, while the bush kauri is of more recent origin.

The best of the pale gums is known as Dial XXXX, with slightly cheaper grades called Rescraped XXX, XX, and X. Cheaper than the above grades, which are very expensive, are No. 1 which is often used in varnishes, and No. 2. The very cheapest grades of kauri resin are called \"chips,\" then \"seeds,\" then \"dust,\" the latter being the poorest of all. The brown kauri in similar grades costs only about two-thirds as much as the other higher grades. Kauri gums at present cost about twice as much as similar grades of Congo resins.

Kauri gum is at present probably the most commonly used fossil gum for varnish manufacture. It makes a very durable high grade varnish, especially for rubbing and polishing. The melting temperature of kauri gum is slightly less than that of the Congo resins, the fusing point of the brown grade being given as 265°C. (509°F.). In the manufacture of varnish, high temperatures of about 350°C. (642°F.) are ordinarily used in order to reduce the weight of the resin and make the melted gum more liquid.

The kauri pine tree bears cones which show that the tree is a Gynnosperm and is related to the pines. There are living kauri pine trees growing in the gum region which exude a soft resin. The fresh gum is said to be of no value to the varnish maker.