Oil painting is the process of painting with pigments with a medium of drying oil as the binder. Used drying oils include linseed oil, poppy seed oil, walnut oil, safflower oil; the choice of oil imparts a range of properties to the oil paint, such as the amount of yellowing or drying time. Certain differences, depending on the oil, are visible in the sheen of the paints. An artist might use several different oils in the same painting depending on specific pigments and effects desired; the paints themselves develop a particular consistency depending on the medium. The oil may be boiled with a resin, such as pine resin or frankincense, to create a varnish prized for its body and gloss. Although oil paint was first used for Buddhist paintings by painters in western Afghanistan sometime between the fifth and tenth centuries, it did not gain popularity until the 15th century, its practice may have migrated westward during the Middle Ages. Oil paint became the principal medium used for creating artworks as its advantages became known.
The transition began with Early Netherlandish painting in Northern Europe, by the height of the Renaissance oil painting techniques had completely replaced the use of tempera paints in the majority of Europe. In recent years, water miscible. Water-soluble paints are either engineered or an emulsifier has been added that allows them to be thinned with water rather than paint thinner, allows, when sufficiently diluted fast drying times when compared with traditional oils. Traditional oil painting techniques begin with the artist sketching the subject onto the canvas with charcoal or thinned paint. Oil paint is mixed with linseed oil, artist grade mineral spirits, or other solvents to make the paint thinner, faster or slower-drying. A basic rule of oil paint application is'fat over lean', meaning that each additional layer of paint should contain more oil than the layer below to allow proper drying. If each additional layer contains less oil, the final painting will peel; this rule does not ensure permanence.
There are many other media that can be used with the oil, including cold wax and varnishes. These additional media can aid the painter in adjusting the translucency of the paint, the sheen of the paint, the density or'body' of the paint, the ability of the paint to hold or conceal the brushstroke; these aspects of the paint are related to the expressive capacity of oil paint. Traditionally, paint was transferred to the painting surface using paintbrushes, but there are other methods, including using palette knives and rags. Oil paint remains wet longer than many other types of artists' materials, enabling the artist to change the color, texture or form of the figure. At times, the painter might remove an entire layer of paint and begin anew; this can be done with a rag and some turpentine for a time while the paint is wet, but after a while the hardened layer must be scraped. Oil paint dries by oxidation, not evaporation, is dry to the touch within a span of two weeks, it is dry enough to be varnished in six months to a year.
Although the history of tempera and related media in Europe indicates that oil painting was discovered there independently, there is evidence that oil painting was used earlier in Afghanistan. Outdoor surfaces and surfaces like shields—both those used in tournaments and those hung as decorations—were more durable when painted in oil-based media than when painted in the traditional tempera paints. Most Renaissance sources, in particular Vasari, credited northern European painters of the 15th century, Jan van Eyck in particular, with the "invention" of painting with oil media on wood panel supports. However, Theophilus gives instructions for oil-based painting in his treatise, On Various Arts, written in 1125. At this period, it was used for painting sculptures and wood fittings especially for outdoor use. However, early Netherlandish painting with artists like Van Eyck and Robert Campin in the 15th century were the first to make oil the usual painting medium, explore the use of layers and glazes, followed by the rest of Northern Europe, only Italy.
Early works were still panel paintings on wood, but around the end of the 15th century canvas became more popular as the support, as it was cheaper, easier to transport, allowed larger works, did not require complicated preliminary layers of gesso. Venice, where sail-canvas was available, was a leader in the move to canvas. Small cabinet paintings were made on metal copper plates; these supports were more expensive but firm, allowing intricately fine detail. Printing plates from printmaking were reused for this purpose; the popularity of oil spread through Italy from the North, starting in Venice in the late 15th century. By 1540, the previous method for painting on panel had become all but extinct, although Italians continued to use chalk-based fresco for wall paintings, less successful and durable in damper northern climates; the linseed oil itself comes from a common fiber crop. Linen, a "support" for oil painting comes from the flax plant. Safflower oil or the walnut or poppyseed oil are sometimes used in formulating lighter colors li
Ochre or ocher is a natural clay earth pigment, a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep brown, it is the name of the colours produced by this pigment a light brownish-yellow. A variant of ochre containing a large amount of hematite, or dehydrated iron oxide, has a reddish tint known as "red ochre"; the word ochre describes clays colored with iron oxide, derived during the extraction of tin and copper. Ochre is a family of earth pigments, which includes yellow ochre, red ochre, purple ochre and umber; the major ingredient of all the ochres is iron oxide-hydroxide, known as limonite, which gives them a yellow colour. Yellow ochre, FeO·nH2O, is a hydrated iron hydroxide called gold ochre. Red ochre, Fe2O3, takes its reddish colour from the mineral hematite, an anhydrous iron oxide. Purple ochre, is identical to red ochre chemically but of a different hue caused by different light diffraction properties associated with a greater average particle size.
Brown ochre FeO, is a hydrated iron oxide. Sienna contains both limonite and a small amount of manganese oxide, which makes it darker than ochre. Umber pigments contain a larger proportion of manganese; when natural sienna and umber pigments are heated, they are dehydrated and some of the limonite is transformed into hematite, giving them more reddish colours, called burnt sienna and burnt umber. Ochres are non-toxic and can be used to make an oil paint that dries and covers surfaces thoroughly. Modern ochre pigments are made using synthetic iron oxide. Pigments which use natural ochre pigments indicate it with the name PY-43 on the label, following the Colour Index International system; the use of ochre is intensive: it is not unusual to find a layer of the cave floor impregnated with a purplish red to a depth of eight inches. The size of these ochre deposits raises a problem not yet solved; the colouring is so intense that all the loose ground seems to consist of ochre. One can imagine that the Aurignacians painted their bodies red, dyed their animal skins, coated their weapons, sprinkled the ground of their dwellings, that a paste of ochre was used for decorative purposes in every phase of their domestic life.
We must assume no less, if we are to account for the veritable mines of ochre on which some of them lived... Iron oxide is one of the most common minerals found on earth, there is much evidence that yellow and red ochre pigment was used in prehistoric and ancient times by many different civilizations on different continents. Pieces of ochre engraved with abstract designs have been found at the site of the Blombos Cave in South Africa, dated to around 75,000 years ago; the practice of ochre painting was prevalent in ancient Australia. Pleistocene burials with red ochre date as early as 40,000 BP and ochre played a role in expressing symbolic ideologies of the earliest arrivals to the continent. In Wales, the paleolithic burial called the Red Lady of Paviland from its coating of red ochre has been dated to around 33,000 years before present. Paintings of animals made with red and yellow ochre pigments have been found in paleolithic sites at Pech Merle in France, the cave of Altamira in Spain; the cave of Lascaux has an image of a horse coloured with yellow ochre estimated to be 17,300 years old.
According to some scholars, Neolithic burials used red ochre pigments symbolically, either to represent a return to the earth or as a form of ritual rebirth, in which the colour symbolises blood and the Great Goddess. In Ancient Egypt, yellow was associated with gold, considered to be eternal and indestructible; the skin and bones of the gods were believed to be made of gold. The Egyptians used yellow ochre extensively in tomb painting, though they used orpiment, which made a brilliant colour, but was toxic, since it was made with arsenic. In tomb paintings, men were always shown with brown faces, women with yellow ochre or gold faces. Red ochre in Ancient Egypt was used as a rouge. Ochre-coloured lines were discovered on the Unfinished Obelisk at the northern region of the Aswan Stone Quarry, marking work sites. Ochre clays were used medicinally in Ancient Egypt: such use is described in the Ebers Papyrus from Egypt, dating to about 1550 BC. Ochre was the most used pigment for painting walls in the ancient Mediterranean world.
In Ancient Greece, red ochre was called μίλτος, míltos. In Athens when Assembly was called, a contingent of public slaves would sweep the open space of the Agora with ropes dipped in miltos: those citizens that loitered there instead of moving to the Assembly area would risk having their clothes stained with the paint; this prevented them from wearing these clothes in public again, as failure to attend the Assembly incurred a fine. It was known as "raddle", "reddle" or "ruddle" and was used to mark sheep and can be used as a waxy waterproof coating on structures; the reddle was sold as a ready-made mixture to farmers and herders by travelling workers called reddlemen. A reddleman named Diggory Venn was prominently described in Thomas Hardy's 1878 novel entitled The Return of the Native. In classical antiquity, the finest red ochre came from a Greek colony on the Black Sea where the modern city of Sinop in Turkey is located, it was regulated and marked by a special seal
Sienna is an earth pigment containing iron oxide and manganese oxide. In its natural state, it is called raw sienna; when heated, it is called burnt sienna. It takes its name from the city-state of Siena. Along with ochre and umber, it was one of the first pigments to be used by humans, is found in many cave paintings. Since the Renaissance, it has been one of the brown pigments most used by artists; the first recorded use of sienna as a colour name in English was in 1760. Like the other earth colours, such as yellow ochre and umber, sienna is a clay containing iron oxide, called limonite, which in its natural state has a yellowish colour. In addition to iron oxide, natural or raw sienna contains about five percent of manganese oxide, which makes it darker than ochre; when heated, the iron oxide is dehydrated and turns to haematite, which gives it a reddish-brown colour. Sienna is lighter in shade than raw umber, clay with iron oxide, but which has a higher content of manganese which makes it greenish brown or dark brown.
When heated, raw umber becomes burnt umber, a dark brown. The pigment sienna was used, in its natural form, by the ancient Romans, it was mined near Arcidosso under Sienese control, now in the province of Grosseto, on Monte Amiata in southern Tuscany. It was called terra gialla, or terra di Siena. During the Renaissance, it was noted by the most read author about painting techniques, Giorgio Vasari, under the name terra rossa, it became, along with umber and yellow ochre, one of the standard browns used by artists from the 16th to 19th centuries, including Caravaggio and Rembrandt, who used all the earth colours, including ochre and umber, in his palette. By the 1940s, the traditional sources in Italy were nearly exhausted. Much of today's sienna production is carried out in the Italian islands of Sardinia and Sicily, while other major deposits are found in the Appalachian Mountains, where it is found alongside the region's iron deposits, it is still produced in the French Ardennes, in the small town of Bonne Fontaine near Ecordal.
In the 20th century, pigments began to be produced using synthetic iron oxide rather than the natural earth. The labels on paint tubes indicate whether they contain synthetic ingredients. PY-43 indicates natural raw sienna, PR-102 indicates natural burnt sienna. There is no single agreed standard for the colour of sienna, the name is used today for a wide variety of hues and shades, they vary by country and colour list, there are many proprietary variations offered by paint companies. The colour box at the top of the article shows one variation from the ISCC-NBS colour list. Raw sienna is a yellowish-brown natural earth pigment, composed of iron oxide hydroxide; the box shows the colour of raw state. It contains a small quantity of manganese oxide; this kind of pigment is known as yellow earth, limonite, or terra gialla. The pigment name for natural raw sienna from the Colour Index International, shown on the labels of oil paints, is PY-43; this box at rights shows a variation of raw sienna from the Italian Ferrario 1919 colour list.
Burnt sienna contains a large proportion of anhydrous iron oxide. It is made by heating raw sienna, which dehydrates the iron oxide, changing it to haematite, giving it rich reddish-brown colour; the pigment is known as red earth, red ochre, terra rossa. On the Colour Index International, the pigment is known as PR-102; this version is from the Italian Ferrario 1919 colour list. The first recorded use of burnt sienna as a colour name in English was in 1853; this variation of burnt sienna is from the Maerz and Paul "A Dictionary of Color" from 1930. It is lighter than most other versions of burnt sienna, it was a mix of burnt raw sienna. This infobox shows the colour dark sienna; this variation is from the ISCC-NBS colour list. A similar dark sienna paint was used on Bob Ross' TV show, The Joy of Painting; the web colour sienna is defined by the list of X11 colours used in web design. Clay earth pigment List of colours List of inorganic pigments
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
Indigenous Australians are the Aboriginal and Torres Strait Islander peoples of Australia, descended from groups that existed in Australia and surrounding islands before British colonisation. The time of arrival of the first Indigenous Australians is a matter of debate among researchers; the earliest conclusively human remains found in Australia are those of Mungo Man LM3 and Mungo Lady, which have been dated to around 50,000 years BP. Recent archaeological evidence from the analysis of charcoal and artefacts revealing human use suggests a date as early as 65,000 BP. Luminescence dating has suggested habitation in Arnhem Land as far back as 60,000 years BP. Genetic research has inferred a date of habitation as early as 80,000 years BP. Other estimates have ranged up to 100,000 years and 125,000 years BP. Although there are a number of commonalities between Indigenous Aboriginal Australians, there is a great diversity among different Indigenous communities and societies in Australia, each with its own mixture of cultures and languages.
In present-day Australia these groups are further divided into local communities. At the time of initial European settlement, over 250 languages were spoken. Aboriginal people today speak English, with Aboriginal phrases and words being added to create Australian Aboriginal English; the population of Indigenous Australians at the time of permanent European settlement is contentious and has been estimated at between 318,000 and 1,000,000 with the distribution being similar to that of the current Australian population, the majority living in the south-east, centred along the Murray River. A population collapse principally from disease followed European settlement beginning with a smallpox epidemic spreading three years after the arrival of Europeans. Massacres and war by British settlers contributed to depopulation; the characterisation of this violence as genocide is controversial and disputed. Since 1995, the Australian Aboriginal Flag and the Torres Strait Islander Flag have been among the official flags of Australia.
The word aboriginal has been in the English language since at least the 16th century to mean, "first or earliest known, indigenous". It comes from the Latin word aborigines, derived from origo; the word was used in Australia to describe its indigenous peoples as early as 1789. It soon became employed as the common name to refer to all Indigenous Australians. While the term Indigenous Australians, has grown since the 1980s to be more inclusive of Torres Strait Islander people, many Aboriginal and Torres Strait Islander peoples dislike it, feeling that it is too generic and removes their identity. Being more specific, for example naming the language group, is considered best practice and most respectful. Terms that are considered disrespectful include Aborigine and ATSI The broad term Aboriginal Australians includes many regional groups that identify under names from local Indigenous languages; these include: Murrawarri people -- see Murawari language. Anindilyakwa on Groote Eylandt off Arnhem Land.
These larger groups may be further subdivided. It is estimated that before the arrival of British settlers, the population of Indigenous Australians was 318,000–750,000 across the continent; the Torres Strait Islanders possess a heritage and cultural history distinct from Aboriginal traditions. The eastern Torres Strait Islanders in particular are related to the Papuan peoples of New Guinea, speak a Papuan language. Accordingly, they are not included under the designation "Aboriginal Australians"; this has been another factor in the promotion of the more inclusive term "Indigenous Australians". Six percent of Indigenous Australians identify themselves as Torres Strait Islanders. A further 4% of Indigenous Australians identify themselves as having both Torres Strait Islander and Aboriginal heritage; the Torres Strait Islands comprise over 100 islands which were annexed by Queensland in 1879. Many Indigenous organisations incorporate the phrase "Aboriginal and Torres Strait Islander" to highlight the distinctiveness and importance of Torres Strait Islanders in Australia's Indigenous population.
Eddie Mabo was from "Mer" or Murray Island in the Torres Strait, which the famous Mabo decision of 1992 involved. The term "black" has been used to refer to Indigenous Australians since European settlement. While related to skin colour, the term is used today to indicate Aboriginal he
Umber is a natural brown or reddish-brown earth pigment that contains iron oxide and manganese oxide. Umber is darker than the other similar earth pigments and sienna. In its natural form, it is called raw umber; when heated, the color becomes more intense, becomes known as burnt umber. The name comes from earth of Umbria, the Italian name of the pigment. Umbria is a mountainous region in central Italy where the pigment was extracted; the word may be related to the Latin word Umbra. Umber is not one precise color, but a range of different colors, from medium to dark, from yellowish to reddish to grayish; the color of the natural earth depends upon the amount of iron manganese in the clay. Umber earth pigments contain between five and twenty percent manganese oxide, which accounts for their being a darker color than yellow ochre or sienna. Commercial colors vary depending upon the color list. Not all umber pigments contain natural earths. Pigments containing the natural umber earths indicate them on the label as PBr7, following the Colour Index International system.
The color shown in the box at right is one of the many commercial varieties of umber, from the ISCC-NBS color list: ISCC-NBS Dictionary of Color Names —Color Sample of Umber. Umber was one of the first pigments used by humans. Dark brown pigments were used in Medieval art; the umbers were not used in Europe before the end of the fifteenth century. The great age of umber was the baroque period, where it provided the dark shades in the chiaroscuro style of painting, it was an important part of the palette of Rembrandt. Rembrandt used it as an important element of his rich and complex browns, he took advantage of its other qualities; the Dutch artist Johannes Vermeer used umber to create shadows on whitewashed walls that were warmer and more harmonious than those created with black pigment. In the second half of the 19th century, the Impressionists rebelled against the use of umber and other earth colors. Camille Pissarro denounced the "old, dull earth colors" and said he had banned them from his palette.
The impressionists chose to make their own browns from mixtures of red, green and other pigments the new synthetic pigments such as cobalt blue and emerald green that had just been introduced. In the 20th century, natural umber pigments began to be replaced by pigments made with synthetic iron oxide and manganese oxide. Natural umber pigments are still being made, with Cyprus as a prominent source. Pigments containing the natural earths are labeled as PBr7, or Brown pigment 7. Displayed at the right is one version of the color raw umber; the source of this color is: ISCC-NBS Dictionary of Color Names —Color Sample of Raw Umber. Burnt umber is made by heating raw umber, which dehydrates the iron oxides and changes them to the more reddish hematite. It's used for both water color paint; the first recorded use of burnt umber as a color name in English was in 1650. Brown List of colors List of inorganic pigments Roelofs, Isabelle. La couleur expliquée aux artistes. Editions Eyrolles. ISBN 978-2-212-13486-5.
Ball, Philip. Histoire vivante des couleurs. Paris: Hazan Publishers. ISBN 978-2-754105-033. Thompson, Daniel V.. The Materials and Techniques of Medieval Painting. Dover. ISBN 0-486-20327-1. "Raw Umber". Essential Vermeer. — Discussion of umber and its use by Vermeer and other painters
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxyhydroxides. Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, are used by humans, e.g. as iron ores, catalysts, in thermite and hemoglobin. Common rust is a form of iron oxide. Iron oxides are used as inexpensive, durable pigments in paints and colored concretes. Colors available are in the "earthy" end of the yellow/orange/red/brown/black range; when used as a food coloring, it has E number E172. Oxide of FeIIFeO: iron oxide, wüstite FeO2: iron dioxide Mixed oxides of FeII and FeIIIFe3O4: Iron oxide, magnetite Fe4O5 Fe5O6 Fe5O7 Fe25O32 Fe13O19 Oxide of FeIIIFe2O3: iron oxide α-Fe2O3: alpha phase, hematite β-Fe2O3: beta phase γ-Fe2O3: gamma phase, maghemite ε-Fe2O3: epsilon phase iron hydroxide iron hydroxide, akaganéite, feroxyhyte, ferrihydrite, or 5 Fe 2 O 3 ⋅ 9 H 2 O, better recast as FeOOH ⋅ 0.4 H 2 O high-pressure FeOOH schwertmannite green rust Several species of bacteria, including Shewanella oneidensis, Geobacter sulfurreducens and Geobacter metallireducens, metabolically utilize solid iron oxides as a terminal electron acceptor, reducing Fe oxides to Fe containing oxides.
Under conditions favoring iron reduction, the process of iron oxide reduction can replace at least 80% of methane production occurring by methanogenesis. This phenomenon occurs in a nitrogen-containing environment with low sulfate concentrations. Methanogenesis, an Archaean driven process, is the predominate form of carbon mineralization in sediments at the bottom of the ocean. Methanogenesis completes the decomposition of organic matter to methane; the specific electron donor for iron oxide reduction in this situation is still under debate, but the two potential candidates include either Titanium or compounds present in yeast. The predicted reactions with Titanium serving as the electron donor and phenazine-1-carboxylate serving as an electron shuttle is as follows: Ti-cit + CO2 + 8H+ → CH4 + 2H2O + Ti + cit ΔE = –240 + 300 mV Ti-cit + PCA → PCA + Ti + cit ΔE = –116 + 300 mV PCA + Fe3 → Fe2+ + PCA ΔE = –50 + 116 mV Note: cit = citrate. Titanium is oxidized to Titanium; the reduced form of PCA can reduce the iron hydroxide.
On the other hand when airborne, iron oxides have been shown to harm the lung tissues of living organisms by the formation of hydroxyl radicals, leading to the creation of alkyl radicals. The following reactions occur when Fe2O3 and FeO, hereafter represented as Fe3+ and Fe2+ iron oxide particulates accumulate in the lungs. O2 + e− → O2• –The formation of the superoxide anion is catalyzed by a transmembrane enzyme called NADPH oxidase; the enzyme facilitates the transport of an electron across the plasma membrane from cytosolic NADPH to extracellular oxygen to produce O2• –. NADPH and FAD are bound to cytoplasmic binding sites on the enzyme. Two electrons from NADPH are transported to FAD which reduces it to FADH2. One electron moves to one of two heme groups in the enzyme within the plane of the membrane; the second electron pushes the first electron to the second heme group so that it can associate with the first heme group. For the transfer to occur, the second heme must be bound to extracellular oxygen, the acceptor of the electron.
This enzyme can be located within the membranes of intracellular organelles allowing the formation of O2• – to occur within organelles. 2O2• – + 2 H+ → H2O2 + O2 The formation of hydrogen peroxide can occur spontaneously when the environment has a lower pH at pH 7.4. The enzyme superoxide dismutase can catalyze this reaction. Once H2O2 has been synthesized, it can diffuse thro