Kauri forests once covered most of the upper North Island of New Zealand; the change of climate, geological activity (volcanic activity and earthquakes) and the impact of Maori and European settlers had led to much deforestation, with some areas reverting to sand dunes, scrub or swamp, but these ancient kauri fields continued to provide a source for gum, as well as the remaining forests.
Kauri gum was formed when resin from the kauri tree leaked out through fractures or cracks in the bark, hardening with the exposure to air. Lumps commonly fell to the ground and became covered with soil and forest litter, eventually fossilising. Other lumps formed as branches forked or trees were damaged, releasing the resin.
The gum varied in colour depending on the condition of the original tree, where it had formed and how long it had been buried. The colours ranged from chalky-white, through red-brown to black; the most prized was a pale gold, 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 some characteristics with amber, another fossilised resin found in the Northern Hemisphere, but where amber can be dated as millions of year old, carbon-dating suggests that the age of most kauri gum is a few thousand years.
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 1840's 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.
It was used to a limited extent in paints during the late nineteenth 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 nineteenth century, sustaining much of the early growth of the city. Between 1850 and 1950, 450,000 tons of gum was exported. 1900 marked the peak in the gum market, with 10,000 tons exported that year, with a value of £600,000. The average annual export was over 5,000 tons, with the average price gained £63 per ton.
By 1850 most of the surface-lying gum had been picked up, and men and women began digging for it. The hillsides yielded shallow-buried gum (about 1m), but in the swamps and beaches it was buried much further down (4m or below).
"The life of a gum-digger is wretched, and one of the last a man would take to."- 1898 gumbuyer
Gum-diggers worked in the old kauri fields, most of which were then covered by swamp or scrub, digging for the gum. Much of the population was transient, moving from field to field, and they lived in rough huts or tents (which were called "whares", after the Maori for 'house'). It was hard work and not very well paid, but it attracted many Maori and European settlers, including women and children. There were many Dalmatians, who had first come to work the South Island goldfields in the 1860s. They were transient workers, rather than settlers, and much of their income was sent out of the country, resulting in much resentment from the local workforce. In 1898 the "Kauri Gum Industry Act" was passed, which reserved gum-grounds for British subjects, and requiring all other diggers to be licenced. By 1910, only British subjects could hold gum-digging licences.
Gumdigging was the major source of income for settlers in Northland, and farmers often worked the gumfields in the winter months to subsidise the poor income from their unbroken land. By the 1890s, 20,000 people were engaged in gumdigging, of which 7000 worked full time. Gumdigging was not restricted to settlers or workers in the rural areas; Auckland families would cross the Waitemata Harbour by ferry at weekends to dig in the fields around Birkenhead, causing damage to public roads and private farms, and leading to local council management of the problem.
Digging in swamps was more complicated; a longer spear (up to 8m) was often used, often fitted with a hooked end to scoop out the lumps. Scrub was often cleared first with fire; some got out of control and swamp fires could burn for weeks.
Holes were often dug by teams in both hills and swamps - often up to 12m deep - and some wetlands were drained to aid in the excavation of gum.
As field gum became scarce, "bush gum" was obtained by purposely cutting the bark of kauri trees and returning months later to retrieve the hardened resin. Due to the damage caused to the trees by the cutting (and climbing, which was done using spikes and hooks), the practice was banned in state forests in 1905.
Gum chips (small lumps useful for the manufacture of linoleum) were difficult to find, and by 1910 the process of washing and sieving to retrieve the chips became common, a process which was later mechanised.
As early as the 1830's and 1840's merchants, including Gilbert Mair and John Logan Campbell, were buying gum from local Maori for £5 a ton, or trading it for goods.