Gum digging was the term used for the excavation of fossilized gum from areas where kauri forests had once grown. Gum digging provided many people with work in New Zealand during the nineteenth century.
Resin made from this gum was of particular importance in the manufacture of slow-drying but hard varnish. After 1900, lower grades were used to make linoleum, but at times it was also used as a substitute for amber in jewellery. More recently small quantities have been used for dentistry.
Before the European settlement the Maoris used the gum as fuel. It was first exported to the USA about 1838 where it was used to make varnish, and by 1853, more than 8,000 tonnes were explored.
Originally, gum exposed above the ground was just collected, but after the gold rush many "diggers" began to obtain gum by digging below the ground. Most of the gum holes can still be found today, untouched and preserved as they were back in the nineteenth century. By 1899, the peak exports were reached wih a total exceeding 11,000 tonnes. As the gum became more difficult to locate, exports dropped, but quantities exceeding several thousand tonnes a year were sold untill the 1940s when synthetics replaced it various uses. In 1971, only 19 tonnes were exported, but they were valued at $NZ12,000.
Sources:
http://www.kauricoast.co.nz/Feature.cfm?WPID=215
http://www.gplatt.demon.co.uk/kauri_gum.htm
http://www.gumdiggerspark.co.nz/story_of_the_gumdiggers.htm