Teacher background information

This elaboration provides a context for students to learn about chemical change and the formation of new substances through exploring the use of chemical reactions by Aboriginal and Torres Strait Islander peoples. Students learn about common everyday chemical reactions such as the organic chemical reactions involved in fermentation, combustion and pyrolysis and inorganic chemical reactions of calcination. Students investigate how Aboriginal and Torres Strait Islander peoples used their organic and inorganic chemistry knowledge to form and utilise new substances, for example, quick lime (calcium oxide), pigments (iron oxide, charcoal), acid (pyroligneous acid), plaster (calcium sulfate), alkali salts (salts of potassium and sodium), beverages (ethanol), charcoal, and by-products such as heat and light. 

Chemical change is a fundamental event and is considered by scientists to be the most crucial process in the universe. Chemical reactions are involved in all aspects of life and occur around us every day. Australia’s First Nations peoples faced and overcame innumerable challenges in the procurement of essential resources. In many areas, important supplies that could not be readily obtained in the required form or could not be traded, had to be produced in situ. This necessity drove the development of sophisticated and complex chemical science practices that utilised chemical reactions to produce the particular substance or product required. Through astute observation many Aboriginal and Torres Strait Islander groups recognised patterns and key variables associated in the formation of new matter. Building on these observations and through empirical evidence acquired through the testing of various techniques, many successful organic and inorganic chemistry processes that produced new matter (required resources) were developed throughout the continent. 

This teacher background information provides information about four documented chemical processes and subsequent products developed and used by Aboriginal and Torres Strait Islander peoples prior to European contact: 

• calcination as used to produce plaster (calcium sulfate) and pigments such as iron oxide 
• pyrolysis used in the production of charcoal, quicklime, pyrolignious acid and salts 
• fermentation in the production of ethanol 
• combustion in the production of heat and light. 

Calcination 

Calcination is a process of heating a substance to change its physical or chemical composition. It involves dehydration, removal of carbon dioxide and sulphur dioxide, and oxidation of part or all of the substance. Calcination requires the firing of the material and is usually carried out in furnaces and kilns. During the process the material is raked over to ensure even heating and effective production of the desired substance. First Nations Australians understood the requirement of carefully controlling the heating process. For example, when using calcination to produce plaster from gypsum, temperatures that are too high will remove all crystalline water from the mineral, rendering it useless. 

Historical accounts record Aboriginal peoples calcining gypsum to produce white pigments for use in paints. In this particular calcination process, calcium sulfate dihydrate (gypsum) was heated in a controlled way until the right amount of the crystalline water was removed to yield a fine white powder to be used as a pigment in paint. 

Plaster was produced across Australia by many First Nations’ groups for various purposes. In the Lake Eyre region of central Australia, gypsum was collected and then calcined to produce plaster that was used to make balls for various ball rolling and spinning games. In the north-west of Queensland, gypsum was calcined to make plaster for use in body ornamentation. 

Pyrolysis 

Pyrolysis is a process of high temperature carbonisation of lignocellulosic biomass in the absence of oxygen. Pyrolysis was traditionally used by First Nations peoples to create numerous important ingredients for various applications, for example, quicklime and pyroligneous acid.  

In central Australia some Aboriginal groups developed a medicine that assisted people in long, arduous journeys. To increase the effectiveness of the active component within this medicine, quicklime (calcium oxide) was procured in the form of ash through the process of pyrolysis. The source of the quicklime is a particular species of plant that was known to contain high levels of calcium oxide, which could be accessed through pyrolyzing its twigs and leaves. The alkali ash produced was mixed with the desiccated and crushed leaves of the medicinal plant. This mixture could be chewed, held in the mouth, or placed behind the ear for extended periods to release its pharmacologically active content orally or transdermally. The alkali ash (quicklime) has the important effect of raising the pH, facilitating the release of the medicine from the plant source and increasing its absorption into the blood stream. 

Pyroligneous acid is a chemical that can be distilled from smoke through the process of pyrolysis. This chemical process was employed by some Palawa women of Tasmania prior to colonisation to procure acid (pyrolignious acid) to use in the removal of periostracum, the thin organic coating of maireener shells, to expose the iridescent nacre. The processed shells were then used in the production of fine necklaces. Commercially available acetic acid (a component of pyroligneous acid which was once a commercial source of acetic acid) is now used by some Palawa women who continue this important practice. 

Another use of pyrolysis by Aboriginal and Torres Strait Islander peoples in the purposeful burning of organic materials is conducted as a means to produce charcoal as an important ingredient in pigments and adhesives.  

Charcoal is particularly useful in the production of various pigments and paints. For this purpose, charcoal is collected, ground into powder, and combined with animal fats to make a paint which can then be applied to the surface to be decorated.  

Charcoal is also used as an additive to change the mechanical properties of some adhesives made from tree gums and resins. These mixtures can then be used to glue items together, such as axe heads or spear heads to shafts. As these resin mixtures are also water-proof they can be used to patch water containers or water craft. 

Charcoal is produced when wood is heated with limited oxygen supply. On heating, water vapour is driven off first. When the temperature increases, the wood carbonises and volatile organic compounds are given off. If this temperature is allowed to rise too high the carbon will also burn and reduce to ash. Charcoal is predominantly carbon with varying amounts of hydrogen and oxygen as well as some minerals, and only forms when the combustion process is incomplete. Careful control of the combustion process is therefore required to produce charcoal as an end-product. 

Historical documents show that Tasmanian Aboriginal People used alkali salts in wood ashes as a substitute for sea salt. It has been widely observed that Aboriginal people living far from sources of sea salt gained this important and much desired ingredient through pyrolysing plant matter in order to release the potassium and sodium bound within its organic matrix of plant matter. Without technology such as titration, plants were empirically investigated and those known to be high in alkali salts such as K or Na were chosen. Aboriginal and Torres Strait Islander peoples employed the process of pyrolysis to access these essential dietary components.  

Fermentation 

Ethanol fermentation, also called alcoholic fermentation, is a biological process in which microorganisms convert sugars such as glucose, fructose and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. 

First Nations peoples have long known how to make alcoholic beverages from nectars and saps prior to the colonisation of Australia. The fermentation processes of First peoples involved the cultivation of unique Australian yeasts and bacteria. A well-known fermentation-derived beverage was developed in Tasmania using the sugar-rich sap of a local Eucalypt known as cider gum. Similarly, Noongar people from south-western Australia exploited certain honey-bearing Banksia species in the production of fermented beverages. 

Combustion 

Combustion is an exothermic chemical reaction between a fuel and an oxidising agent, usually atmospheric oxygen, and typically accompanied by the generation of heat and light in the form of flame. In combustion reactions, the combination of reactants happens at a high rate, in part because more energy is generated than can be transferred into the surrounding medium resulting in the temperature of the reactants being raised to accelerate the reaction even more. 

Aboriginal and Torres Strait Islander peoples also use the combustion of resins and gums derived from a range of trees and shrubs to provide light and to carry fire from campsite to campsite. Various bundles of bark, branches and dried flower heads are smeared with resin or gum and used as torches. These torches assist in navigating at night and are used when burning country. They are also useful for fishing at night, as the fish can be attracted to the light. 

By investigating the chemical processes and subsequent products developed and used by Aboriginal and Torres Strait Islander peoples prior to European contact in producing useful new substances, students will have the opportunity to develop a deeper understanding of chemical change and First Nations peoples’ knowledge and use of organic and inorganic chemistry beyond combustion reactions used in the generation of heat and light.