Kauri gum is resin from kauri trees (Agathis australis), which historically had several important industrial uses. It can also be used to make crafts such as jewellery. Kauri forests once covered much of the North Island of New Zealand, before climate change caused the forests to retreat, causing several areas to revert to sand dunes, scrubs, and swamps. Even afterwards, ancient kauri fields and the remaining forests continued to provide a source for the gum. Between 1820 and 1900, over 90% of Kauri forests were logged or burnt by Europeans.
Kauri gum forms when resin from kauri trees leaks out through fractures or cracks in the bark, hardening with the exposure to air. Lumps commonly fall to the ground and can be covered with soil and forest litter, eventually fossilising. Other lumps form as branches forked or trees are damaged, releasing the resin.
Uses
The Māori had many uses for the gum, which they called kapia. Fresh gum was used as a type of chewing gum (older gum was softened by soaking and mixing with juice of the puha thistle). Highly flammable, the gum was also used as a fire-starter, or bound in flax to act as a torch. Burnt and mixed with animal fat, it made a dark pigment for moko tattooing. Kauri gum was also crafted into jewellery, keepsakes, and small decorative items. Like amber, kauri gum sometimes includes insects and plant material.
Kauri gum was used commercially in varnish, and can be considered a type of copal (the name given to resin used in such a way). Kauri gum was found to be particularly good for this, and from the mid-1840s was exported to London and America. Tentative exports had begun a few years earlier, however, for use in marine glue and as fire-kindlers; gum had even made up part of an export cargo to Australia in 1814.
Since the kauri gum was found to mix more easily with linseed oil, at lower temperatures, than other resins, by the 1890s, 70 percent of all oil varnishes made in England used kauri gum. It was used to a limited extent in paints during the late 19th century, and from 1910 was used extensively in the manufacture of linoleum. From the 1930s, the market for gum dropped as synthetic alternatives were found, but there remained niche uses for the gum in jewellery and specialist high-grade varnish for violins.
Kauri gum was Auckland's main export in the second half of the 19th century, sustaining much of the early growth of the city. Between 1850 and 1950, 450,000 tons of gum were exported. The peak in the gum market was 1899, with 11,116 tons exported that year, with a value of £600,000 ($989,700 US). The average annual export was over 5,000 tons, with the average price gained £63 ($103.91 US) per ton.
Appearance
The gum varied in color depending on the condition of the original tree. It also depended on where the gum had formed and how long it had been buried. Colors ranged from chalky-white, through red-brown to black; the most prized was a pale gold, as it was hard and translucent. The size of each lump also varied greatly. Swamps tended to yield the small nuggets known as "chips", whereas the hillsides tended to produce larger lumps. The majority were the size of acorns, although some were found which weighed a few pounds; the largest (and rarest) were reported to weigh half a hundredweight. Kauri gum shares a few characteristics with amber, another fossilised resin found in the Northern Hemisphere, but where amber can be dated as millions of years old, carbon-dating suggests the age of most kauri gum is a few thousand years.
Gumfields
Most of the gumfields were in Northland, Coromandel and Auckland, the site of the original kauri forests. Initially, the gum was readily accessible, commonly found lying on the ground. Captain Cook reported the presence of resinous lumps on the beach at Mercury Bay, Coromandel, in 1769, although he suspected it came from the mangroves, and missionary Samuel Marsden spoke of their presence in Northland in 1819.
By 1850, most of the surface-lying gum had been picked up, and people began digging for it. The hillsides yielded shallow-buried gum (about 1 m), but in the swamps and beaches, it was buried much further down (4 m or below).
Gum-diggers
Gum-diggers were men and women who dug for kauri gum, a fossilised resin, in the old kauri fields of New Zealand at the end of the 19th and early 20th centuries. The gum was used mainly for varnish. The term may be a source for the nickname "Digger" given to New Zealand soldiers in World War I. In 1898, a gum-digger described "the life of a gum-digger" as "wretched, and one of the last [occupations] a man would take to."