Teacher background information

This elaboration provides students with the opportunity to learn about Aboriginal and Torres Strait Islander Peoples’ knowledge and understanding of how light behaves in contact with different materials. The refraction, reflection and absorption of light as it passes from one substance into another is a phenomenon that Aboriginal and Torres Strait Islander Peoples have long observed. This is evidenced in the various ways that Aboriginal and Torres Strait Islander Peoples counter and utilise light. Such knowledge is critical to accurately spear fish in water and to construct housing that provides optimal protection in the environment. This elaboration provides students with the opportunity to learn about the properties of light and how such knowledge has informed Aboriginal and Torres Strait Islander Peoples’ technologies and practices.

Aboriginal and Torres Strait Islander Peoples have a long and ongoing understanding of the properties of light and how light behaves when it contacts or passes through different materials. When light strikes a surface, the rays may be absorbed and converted to heat energy, reflected into the atmosphere or refracted modifying the optical perception of objects. The optical properties of light are well understood by Aboriginal and Torres Strait Islander Peoples, and have informed the development of many successful practices and technologies for millennia.

Ochre is a mineral that has long been a valuable commodity for Aboriginal Peoples and is used as a pigment for decorative and artistic purposes. The types of ochre that can be mined from different sites across Australia vary in type, quality and colour, and some rare ochres are widely sought after and traded over vast distances. Among the most highly prized ochres are those that have a silvery sheen caused by the admixture of other minerals such as cinnabar (mercury sulfide) or fragments of mica, a silicate mineral. These components have high refractive indexes when compared with air, contributing to a shimmering effect when light passes through the air to ochre.

Cinnabar has the highest refractive index of any known mineral. The Adnyamathanha Peoples of the Flinders Ranges region in South Australia quarried the Parachilna mine for the red ochre deposits that contain such mercury compounds. This ochre was highly prized and Aboriginal Peoples, such as the Dieri Peoples who occupied the lands over 500 kilometres north west of Parachilna, and the Mitakoodi Peoples from the Cloncurry region in Queensland more than 1300 kilometres away, travelled to barter and trade ochre with the Adnyamathanha Peoples. The Wilgie Mia ochre deposits on Wajarri Yamatji Country in Western Australia contain a high mica component, giving the deep red ochre a silvery sheen. This ochre was a widely sought-after ochre of significant value prior to colonisation and remains so today. Aboriginal Peoples utilised the firelight refraction from these precious ochres to create a shimmer effect. Such ochres have long been used, and continue to be used today, as body decoration by Australia’s First Peoples. Mica flakes are an important ingredient in contemporary cosmetic products globally. The tiny particles refract light and cause the popular shimmering effect. The use of mica for cosmetic purposes can be traced back many millennia in Australia.

Aboriginal and Torres Strait Islander Peoples use the understanding of the refraction of light in the practice of spear fishing. Spear fishing is a hunting practice that has been undertaken for many thousands of years by many Aboriginal and Torres Strait Islander Peoples. On Mer Island in the Torres Strait, the Meriam Peoples catch fish by spear fishing in both shallow waters while walking along the shore, and in deeper waters from a boat. The Wardandi Peoples of the Noongar nation in south west Western Australia spear fish in traps set to utilise the changing tide. Prior to colonisation, bark canoes were used for spear fishing along the Murray River at night, and firelight from an elevated scaffold in the centre of the vessel was used to provide light and to attract the fish.

Accurate and successful spear fishing requires an understanding of the behaviour of light as it passes from air into water. Refraction is a phenomenon in which the speed of light slows as it passes into a material of higher optical density, resulting in a change of direction of the path of light. Due to this refraction of light, an object in the water appears higher than its actual position. Consequently, to successfully spear an object, the aim of the spear needs to be adjusted to target a lower position. The degree to which light refracts when it passes from air into water depends on whether it is salt or fresh water and the depth of the water. The deeper the water, the greater the effect of refraction. Therefore, in deep water, a greater adjustment is needed to counter the effects of refraction, and a hunter needs to aim well below its apparent position to successfully spear the fish. These differences are well understood by Aboriginal and Torres Strait Islander Peoples and such knowledge has been used for millennia, and continues to be used, to accurately and successfully hunt fish using spears.  

Aboriginal and Torres Strait Islander Peoples’ knowledge of the properties of light facilitated the construction of shelters prior to colonisation across a range of geographical locations and in varying climatic conditions. Depending on the environment, homes were constructed to provide shade and protection from the heat or to absorb heat to provide insulation against the cold. When light strikes a surface, the rays may be absorbed, reflected or refracted. If the light strikes a light-coloured surface most of the light is reflected, while dark surfaces absorb light which is then converted to heat. Aboriginal and Torres Strait Islander Peoples understand which natural materials absorb or reflect light in the selection of suitable resources to construct shelters to meet their needs. The Warlpiri Peoples of the Tanami Desert north west of Alice Springs construct shade structures known in Warlpiri language as malurnpa. These shelters consist of a wall that is orientated to maximise shade from the sun and remains open on all other sides to allow air flow. These shade walls are constructed using Spinifex spp. or Eucalyptus spp. leaves due to their light silvery colour that maximises the reflection of light, ensuring the shelter provides the best possible protection from the intensity of the sun. Prior to colonisation, the Jardwadjali Peoples in eastern Victoria constructed large circular huts that were entirely coated with clay to protect against the cool climate; the clay served a dual purpose as it absorbed sunlight for warmth and provided insulation to retain warm internal air.

This elaboration provides students with the opportunity to understand Aboriginal and Torres Strait Islander Peoples’ knowledge of the optical properties of light and examples of the technologies and practices that are informed through this knowledge. The application of this knowledge in different technologies and practices demonstrates Aboriginal and Torres Strait Islander Peoples’ understanding of refraction, reflection and absorption. Students will have the opportunity to learn how the historical practices utilising this knowledge in different technologies and practices continue to be of importance in Aboriginal and Torres Strait Islander Peoples’ lives in contemporary Australia.