1. From earliest times, people have used colour to decorate themselves and their surroundings.
Identify the sources of the pigments used in early history as readily available minerals
Pigments available to early artists were derived from natural resources. They are different to dyes, which are usually soluble in water, which stain and run on surfaces.
-White: produced in white clay (kaolin), hydrated aluminium silicate (Al2O3.2SiO2.2H2O); chalk, calcium carbonate; gypsum, calcium dihydrate (CaSO4.2H2O)
-Ochre (natural earth of silica and clay):
- Yellow – various hydrated iron oxides, main one being mineral goethite (Fe2O3.H2O)
- Red – contains anhydrous iron (III) oxide (Fe2O3)
- Brown – nearly pure limonite (FeO(OH))
-Black – naturally occurring manganese (IV) oxide or charcoal, which is mainly graphite, resulted from the burnt wood, animal bones or the soot from lamps.
Explain why pigments used needed to be insoluble in most substances
-Pigments are inorganic (obtained from rock) or organic (obtained from living material) substances of small particles that is insoluble in the applied medium and is used on account of its colouring, protective or magnetic properties.
-Pigments need to not stain and run on surfaces. When exposed to moisture or water, pigments must not be easily dissolved so that it remains adhered to surfaces. Also, cosmetics made from insoluble minerals ensure that it doesn’t dissolve in perspiration. Pigments should also be opaque.
Outline the early uses of pigments for:
cave drawings
-Rock paintings have been produced since the Stone Age. Oldest cave paintings confirmed by radioactive dating are in Chauvet Cave, France. Pigments used include red iron oxide, soot, black manganese oxide and white porcelain clay. These were mixed with cave water, which had high calcium content, ensuring good adhesion and long durability.
-Aborigines used pigments to produce schematic artworks on rocks located near ceremonial sites or corroboree grounds.The pigments were obtained from red and yellow ochre, charcoal, chalk and clay, and mixed with binders that included blood, raw egg, animal fat, sap, honey or wax. Paint applied using fingers, brush or chewed and frayed end of a twig.
self-decoration including cosmetics
-Aboriginal uses of pigments include smearing clay and ochre in geometrical patterns on themselves for ceremonial purposes. Charcoal was sometimes rubbed on foreheads.
-Ancient Egyptians used eye makeup, lipstick and rouge for cosmetic purposes. Kohl was used to darken eyebrows, for eyelashes and sometimes to darken hair. It has also been thought that black eye paint (constitutes Laurionite – PbOHCl and phosgenite – Pb2Cl2CO3) were used as bactericide protection against eye disease in the hot dry Egyptian climate. Laurionite and phosgenite do not occur naturally so they had to synthesise them.
-Ancient Greek women used cerusse (lead carbonate), a white pigment to make their face pale.
-Ancient Romans also used lead carbonate and chalk for face paint and rouge made out of lead oxide.
preparation of the dead for burial
-Pigment has been used in burial sites all around the world, including Qafzeh Cave, funeral contexts in Greece and Spain, Lake Mungo in NSW, and Krems in Austria.
-Red pigment was obtained from Red Ochre. Red is associated with blood and has been thought to symbolise life’s meaning and life over death. Red ochre is a suitable material as a pigment as it is soft, easy to ground in powder and is insoluble.
-Red pigment was also obtained from cinnabar. Cinnabar may have had a role as a preservative due to its toxicity.
-Ancient Egyptian tombs contained corpses painted with a representation of the person and that the walls of the sarcophaguses were painted depicting the history of life. Tutankhamen’s tomb contained samples of gypsum, orpiment, haematite and malachite.
Outline the processes used and the chemistry involved to prepare and attach pigments to surfaces in a named example of medieval or earlier outwork
-“Madonna and the Child with Saints Jerome, John the Baptist, Bernadino and Bartholomew,” by Sano di Petro is 600 years old. Originates from Italy.
-The surface is made of wooden panels – oak, pine or poplar with canvas (linen) glued with animal glue. Gesso is coated. Grosso is the coarser and thicker layer that it painted, with sottiel painted on top as a smooth top surface.Charcoal is used for underdrawing.
-Pigments used include cinnabar (red), azurite (blue), gypsum (white), orpiment (yellow) and malachite (green). Egg tempera used as binders (commonly used in late medieval panel painting)
-Decoration produced by mordant gilding. The area to be gilded is coated with mixture of iron (III) oxide and egg white, which is then polished after it had set hard. The gold leaf applied using glue such as egg white and burnished with a tool.
Explain that colour can be obtained through pigments spread on a surface layer (e.g. paint) or mixed with the bulk of material (e.g. glass colours)
Pigments added onto a surface layer
-Paintings contain layers including wood, canvas, ground layers, drawing, paint layers and varnish. Panels prepared for painting by mixing gypsum or chalk with animal glue. It was applied as a thick warm liquid and set to a creamy white layer which was rubbed smooth.
-Paint layers included pigments mixed with a bind medium or a drying oil. For example, the blue colour of natural ultramarine pigment is maintained within aqueous solutions and egg tempera which binds the pigment.
Mixing with bulk of material
-Glass was made from melted sand (SiO2). This was obtained by adding flux (mixture of sand, soda ash, lime, potash and lead oxide to lower melting point) and heating sand at 800 degrees Celcius.
-Pigments were added to the molten glass, and the pigment disperses and traps in glass as it cools and hardens.Details were painted onto glass with one dark pigment of copper or iron oxide mixed with soft powered glass, then made permanent by firing in kiln. An example of this is stained glass.
Describe paints as consisting of:
the pigment
-Pigments must be chemically inert and should be unaffected by light, heat, acids, moisture or pollution. They impart colour onto surfaces. Pigments are grounded into fine powder and thoroughly mixed and dispersed into the binding liquid.
-Types of pigments include
- Organic pigments – made from animal/vegie sources, are likely to fade eg. Tyrolean purple – marine slug, Lake pigments such as indigo lake, rose madder lake and carmine lake. Benefit of a lake pigment is that it gives a softer colour, although it is unstable when exposed to light.
- Inorganic/mineral pigments – natural pigments prepared from minerals eg. ochre, azurite/malachite. Benefit of inorganic pigment is that it gives a more opaque colour, although many contain toxic heavy metals.
- Synthetic pigment – 19th/20th century produced eg. Prussian blue, Titanium oxide, cadmium yellow. Many are expensive to produce.
a liquid to carry the pigment
-The liquid binding medium is the vehicle that transports the dispersed pigment and binds it onto a surface.
-When the mediumdries, unsaturated bonds crosslink after oxidising to form a three dimensional polymer network. The pigment becomes trapped in the liquid and so it remains adhered onto the surface. The medium should also allow for expansion and contraction so that the paint will not crack.
-Examples:
- Egg tempera – from 14th century. Egg yolk is misted with pigment – tough and long lasting
- Gum Arabic – principle binder in watercolours (plant resin from acacia plants)
- Linseed oils – best of drying agent, specially prepared for use in oil paint
- Alkynols– oil modified synthetic resins, dry quickly and have good adhesive and non-yellowing properties
- Acrylics – used in quick drying synthetic paints. Durable, flexible and suitable for use on paper, panels & unprimed canvas
Describe an historical example to illustrate the relationship between the discovery of new mineral deposits and the increasing range of pigments
-Modern pigment industry started in the 18th century. This increased understanding of reactions and stoichiometry, allowing production conditions such as pH and temperature to be controlled and altered. This increased the range of colours and sizes of pigments available.
-New metals have been discovered, such as cadmium, cobalt, chromium, manganese and molybdenum. New synthetic colour pigments have been produced, such as cadmium red, cadmium yellow, manganese blue, cobalt blue, chrome yellow and molybdenum red. Prussian blue and cobalt blue were developed during this time as an alternative to the expensive Ultramarine blue.
-A specific example is the discovery of an orange-red colour mineral called chrocite (PbCrO4) in 1770s in Siberia, which contained chromium. This mineral is rare. However, discovering large deposits of chromite(FeCr2O4) in US in 1820 led to manufacture of chromium compounds.
-Before the 19th century, yellows were typically compounds of lead, tin and antimony. A richer golden yellow is orpiment, arsenic sulphide.
-Newer yellows include chrome yellow (PbCrO4), strontium chromate (pale yellow), barium chromate (lemon yellow), zinc chromate (greenish yellow). These have replaced toxic yellow orpiment.
Analyse the relationship between the chemical composition of selected pigments and the position of the metallic component(s) of each pigment in the periodic table
Most colour pigments are sulfides or oxides of transition metals.
Pigment / Composition / Colour / MetalNaples Yellow / Antimony oxide / yellow / Sb (group V)
Yellow orpiment / Arsenic (III) sulfide / Yellow / As (group V)
Malachite / Copper carbonate / Green / Cu (transition)
Azurite / Copper carbonate / Blue / Cu (transition)
Haematite / Iron oxide / Red / Fe (transition)
Limonite / Iron oxide / Brown / Fe (transition)
Cinnabar / Mercury Sulfide / red / Hg (transition)
Zinc white / Zinc oxide / white / Zn (transition)
Solve problems and perform a first hand investigation or process information from secondary sources to identify minerals that have been used as pigments and describe their chemical composition with particular reference to pigments available and used in traditional art by Aboriginal people.
-Pigments are mineral salts(oxides, phosphates, carbonates.) Naturally occurring and insoluble
-Differences is the colour of ochre is due to the presence of different amounts of oxyhydroxides (mainly goethite) and oxides (hematite)
-Water is driven off when siennas and umbers are placed in a fire, changing the colour.
-Kaolinite is a soft clay silicate mineral produced by chemical weathering of aluminium silicate minerals like feldspar
Colour / Name of Pigment / Chemical CompoundRed / Red Ochre / Fe2O3
Yellow / Yellow Ochre / Fe2O3.H2O
Brown / Brown Ochre / FeO(OH)
Deep Brown / Umber / Fe203 (45-70%)Manganese Dioxide (5-20%)
Red Brown / Sienna / Fe2O3 (50%)Manganese Dioxide (<1%)
White / Kaolin
Chalk
Gypsum / Al2Si2O5(OH)4
CaCO3 (50-98%) and various minerals (clay, hematite, mica, quartz and pyrite)
CaSO4.2H2O
Black / Manganese (IV) Oxide
Charcoal
Bone Black / MnO2
Carbon
Carbon (10-20%)Ca3(PO4)2 (70-80%)
Process information from secondary sources to identify the chemical composition of identified cosmetics used in an ancient culture such as early Egyptian or Roman and use available evidence to assess the potential health risk associated with their use.
Colour / Name of Pigment / Chemical CompoundGreen-Blue / Malachite / CuCO3.Cu(OH)2
Black / Galena
Cerussite / PbS
PbCO3
Yellow & Red / Yellow Orpiment
Red Orpiment / Ag2S3
AsS
Red / Cinnabar
Vermillion / HgS
White / White lead / 2PbCO3.Pb(OH)2
-Ancient Egyptians used red pigment for rouge and lipstick, and green, blue, black and yellow pigments in eye makeup.Ancient Romans used white lead as face powders and vermillion (HgS) as red makeup.
-Orpiment contains Arsenic. Acute toxicity (immediate) is high for inorganic arsenic compounds, with symptoms including nausea, diarrhoea, cyanosis, hallucinations and cardiac arrhythmia. Symptoms of chronic arsenic poisoning include depression, numbness, sleeping disorders and headaches.
-Mercury is a cumulative poison that is highly toxic by ingestion and inhalation in high doses. Early symptoms may include irritability, excitability and insomnia. With long lasting exposure, tremors develop, causing severe behavioural and personality changes and loss of memory, severely affecting the central and peripheral nervous system
-Malachite may cause gastrointestinal discomfort: may be harmful if inhaled; eye irritant
-Galena contains lead which is a cumulative poison that can lead to abdominal pain, muscular weakness and fatigue and headache. It can cause nervous system disorders.
-White lead is a cumulative poison that is toxic by inhalation and ingestion, causing brain damage in children and irritating skin, eye and lungs.
-Use of these pigments were harmful as they were used on skin, so they would have been affected by the symptoms described due to prolonged accumulation of these poisonous chemicals
Identify data, gather and process information from secondary sources to identify and analyse the chemical composition of an identified range of pigments.
Time Period / Name of Pigment / Type of pigment / Colour / Chemical CompositionPrehistoric / Ochre / Natural Inorganic / Red
Yellow / Fe2O3
FeO(OH)
Umber / Natural Inorganic / Brown / Fe2O3 (45-70%)MnO2 (15-20%)
Chalk White / Natural inorganic / White / CaCO3
Ancient Civilisations / Cinnabar / Natural inorganic / Red / HgS
Vermillon / Synthetic inorganic / Red / Hgs
Orpiment / Natural inorganic / Red
Yellow / AsS
As2S3
Malachite / Natural inorganic / Green / CuCO3.5H2O
Madder / Natural organic / Red / C14H8O4.C14H8O5
Indigo / Natural organic / Blue / C16H10N2O2
Medieval / Naples Yellow / Synthetic inorganic / Yellow / Pb(SbO3)2 or Pb(SbO4)2
Carmine Lake / Natural organic / Red / C22H20O13, C16H10O8
Smalt / Synthetic inorganic / Blue / CoO in silicate
Ultramarine Blue / Natural inorganic / Blue / Na8Al6Si6O24S2
Modern / Synthetic Ultramarine Blue / Synthetic inorganic / Blue / -
Alizarin / Synthetic organic / Red / C14H8O4.C14H8O5
Cobalt Blue / Synthetic inorganic / Blue / CoO.Al2O3
Chrome Yellow / Synthetic inorganic / Yellow / PbCrO4
Titanium White / Refined mineral / White / TiO2
2. By the twentieth century, chemists were using a range of technologies to study the spectra, leading to increased understanding about the origins of colours of different elements.
Identify Na+, K+, Ca2+, Ba2+, Sr2+ and Cu2+ by their flame colour.
Name of Element / Cation / Colour in flame / Colour through blue glassSodium / Na+ / Yellow / Colourless
Potassium / K+ / Violet / Purple red
Calcium / Ca2+ / Brick Red / Greenish
Barium / Ba2+ / Yellow Green
Strontium / Sr2+ / Scarlet Red / Violet
Copper / Cu2+ / Emerald Green
Perform first-hand investigation to observe the flame colour of Na+, K+, Ca2+, Ba2+, Sr2+ and Cu2+.
-Qualitative test determining the identity or possible identity of a metal or metalloid ion
-Pour 10ml conc. HCL into 50 mL beaker. HCl is used to clean the wire, as impurities will make results incorrect.
-Caution: HCl is highly corrosive and so it irritates eyes and skin, possibly causing burns if contacted. If ingested,lining of lungs and oesophagus may be damaged. Wear safety glasses and protective shoes and clothing.
-Dip platinum wire loop in the acid and rinse with distilled water, and heat the loop in the outer edge of the burner flames. Continue until no colour is observed in flame.
-Dip clean wire loop into one of nitrate powders. Place loop in outer eye of burner flame and move loop up and down. Note colour of flame.
-Repeat with a different nitrate powder.
-Cobalt blue glass filters out yellow colour (particularly Na+), allowing some flame colours to be identified.
Explain the flame colour in terms of electrons releasing energy as they move to a lower energy level.
-An atom does not radiate energy when its electrons are in a fixed orbit
-Electrons move from a lower orbit to a higher orbit if it is given energy by an external source. The orbit that it jumps to depends on the amount of energy the electron absorbs. The energy is absorbed as a photon of electro-magnetic radiation. The photons energy equals the difference in energy between the two stationary states of orbit.
-The colour of a flame is created by a strong emission in the line spectrum of the element.
-The electron will not remain in this orbit, but will decay back to its original orbit. They decay may be in a single or multiple steps. Each time the electron decays to original orbit, energy is loss and a photon in emitted. The specific wavelength of colour of the photon depends on amount of energy loss.
Identify that, as electrons return to lower energy levels, they emit quanta of energy which humans may detect as a specific colour.
-The wavelength of EM radiation depends on the energy difference between the energy levels
-In hydrogen the visible wavelength are called the Balmer series, referring to the transitions from 3rd, 4th, 5th or 6th level to the 2nd (n=2) level. The human eye is sensitive to the visible region of the EM spectrum. Different effects of infra-red and ultraviolet are due to difference in the energy of the radiation.
Explain why excited atoms only emit certain frequencies of radiation.
-When an electron drops from an orbit farther from the nucleus to one closer to the nucleus, it emits a photon of specific energy.
-Unlike white light from sun, light given off by an energetically excited atom is not a continuous distribution of wavelengths. When passed through a narrow slit and then through a prism, visible light emitted by an excited atom is found to consist only of a few wavelengths.
-The energy is not continuous but is quantised, that is electrons can be in one fixed orbit or another fixed orbit, but not between orbits. Each of the orbits relate to a certain energy level of the electron.
-The excited atoms emit certain frequencies of radiation (photons) because the differences between energy levels of the orbits are fixed.
-Planck proposed that electromagnetic radiation is transmitted and absorbed in discrete units, or quanta, called photons. Energy carried by a photon of radiation is proportional to frequency. Greater the difference in orbit radius, greater is the energy of the emitted photon. Amount of energy between two energy levels is calculated using equation: E = hf, where h is Planck’s constant