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Concept
Kauri gum
Résumé
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.
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.
Source officielle
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