Pear-shaped is a metaphorical term with several meanings, all in reference to the shape of a pear, i.e. tapering towards the top. The comparison is more or less literal when the term is applied to people, where it means narrow at the shoulders and wide at the hips, a use that goes back to at least 1815, one that can have either positive connotations or negative, depending upon the context. In the 20th century, more abstract use of the term evolved; when said of someone's voice, "pear-shaped" means sonorous. The Oxford English Dictionary dates this use to 1925; the third meaning is limited to the United Kingdom Ireland, South Africa and Australasia. It describes a situation that went awry horribly so. A failed bank robbery, for example, could be said to have "gone pear-shaped"; the origin for this use of the term is in dispute. The OED cites its origin as within the Royal Air Force as a cleaned-up alternative version of its phrase "tits-up" meaning broken or dead.
The neutron is a subatomic particle, symbol n or n0, with no net electric charge and a mass larger than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave within the nucleus, each has a mass of one atomic mass unit, they are both referred to as nucleons, their properties and interactions are described by nuclear physics. The chemical and nuclear properties of the nucleus are determined by the number of protons, called the atomic number, the number of neutrons, called the neutron number; the atomic mass number is the total number of nucleons. For example, carbon has atomic number 6, its abundant carbon-12 isotope has 6 neutrons, whereas its rare carbon-13 isotope has 7 neutrons; some elements occur in nature with only one stable isotope, such as fluorine. Other elements occur with many stable isotopes, such as tin with ten stable isotopes. Within the nucleus and neutrons are bound together through the nuclear force. Neutrons are required for the stability of nuclei, with the exception of the single-proton hydrogen atom.
Neutrons are produced copiously in nuclear fusion. They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission and neutron capture processes; the neutron is essential to the production of nuclear power. In the decade after the neutron was discovered by James Chadwick in 1932, neutrons were used to induce many different types of nuclear transmutations. With the discovery of nuclear fission in 1938, it was realized that, if a fission event produced neutrons, each of these neutrons might cause further fission events, etc. in a cascade known as a nuclear chain reaction. These events and findings led to the first self-sustaining nuclear reactor and the first nuclear weapon. Free neutrons, while not directly ionizing atoms, cause ionizing radiation; as such they can be a biological hazard, depending upon dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers, by the natural radioactivity of spontaneously fissionable elements in the Earth's crust.
Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scattering experiments. An atomic nucleus is formed by a number of protons, Z, a number of neutrons, N, bound together by the nuclear force; the atomic number defines the chemical properties of the atom, the neutron number determines the isotope or nuclide. The terms isotope and nuclide are used synonymously, but they refer to chemical and nuclear properties, respectively. Speaking, isotopes are two or more nuclides with the same number of protons; the atomic mass number, symbol A, equals Z+N. Nuclides with the same atomic mass number are called isobars; the nucleus of the most common isotope of the hydrogen atom is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium and tritium contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons.
The most common nuclide of the common chemical element lead, 208Pb, has 82 protons and 126 neutrons, for example. The table of nuclides comprises all the known nuclides. Though it is not a chemical element, the neutron is included in this table; the free neutron has 1.674927471 × 10 − 27 kg, or 1.00866491588 u. The neutron has a mean square radius of about 0.8×10−15 m, or 0.8 fm, it is a spin-½ fermion. The neutron has no measurable electric charge. With its positive electric charge, the proton is directly influenced by electric fields, whereas the neutron is unaffected by electric fields; the neutron has a magnetic moment, however. The neutron's magnetic moment has a negative value, because its orientation is opposite to the neutron's spin. A free neutron is unstable, decaying to a proton and antineutrino with a mean lifetime of just under 15 minutes; this radioactive decay, known as beta decay, is possible because the mass of the neutron is greater than the proton. The free proton is stable. Neutrons or protons bound in a nucleus can be stable or unstable, depending on the nuclide.
Beta decay, in which neutrons decay to protons, or vice versa, is governed by the weak force, it requires the emission or absorption of electrons and neutrinos, or their antiparticles. Protons and neutrons behave identically under the influence of the nuclear force within the nucleus; the concept of isospin, in which the proton and neutron are viewed as two quantum states of the same particle, is used to model the interactions of nucleons by the nuclear or weak forces. Because of the strength of the nuclear force at short distances, the binding energy of nucleons is more than seven orders of magnitude larger than the electromagnetic energy binding electrons in atoms. Nuclear reactions therefore have an energy density, more than ten million times that of chemical reactions; because of the mass–energy equivalence, nuclear binding energies reduce the mass of nuclei. The ability of the nuclear force to store energy arising from the electromagnetic repulsion of nuclear components is the basis for most of the energy that makes nuclear reactors or bombs possible.
In nuclear fission, the absorption of a neutron by a heavy nuclide causes the nuclide to become unstable and break into light nuclides and additional neu
Lesotho the Kingdom of Lesotho, is an enclaved country–the only one in the world outside of the Italian peninsula–within the border of South Africa. It has a population of around 2 million, its capital and largest city is Maseru. Lesotho was the British Crown Colony of Basutoland, but it declared independence from the United Kingdom on 4 October 1966, it is now a sovereign state, a member of the United Nations, the Commonwealth of Nations, the Southern African Development Community. The name Lesotho translates to "the land of the people who speak Sesotho"; the original inhabitants of the area now known as Lesotho were the San people. Examples of their rock art can be found in the mountains throughout the area; the present Lesotho called Basutoland, emerged as a single polity under King Moshoeshoe I in 1822. Moshoeshoe, a son of Mokhachane, a minor chief of the Bakoteli lineage, formed his own clan and became a chief around 1804. Between 1821 and 1823, he and his followers settled at the Butha-Buthe Mountain, joining with former adversaries in resistance against the Lifaqane associated with the reign of Shaka Zulu from 1818 to 1828.
Subsequent evolution of the state hinged on conflicts between British and Dutch colonists leaving the Cape Colony following its seizure from the French-allied Dutch by the British in 1795, subsequently associated with the Orange River Sovereignty and subsequent Orange Free State. Missionaries invited by Moshoeshoe I, Thomas Arbousset, Eugène Casalis and Constant Gosselin from the Paris Evangelical Missionary Society, placed at Morija, developed orthography and printed works in the Sesotho language between 1837 and 1855. Casalis, acting as translator and providing advice on foreign affairs, helped to set up diplomatic channels and acquire guns for use against the encroaching Europeans and the Griqua people. Trekboers from the Cape Colony arrived on the western borders of Basutoland and claimed land rights, beginning with Jan de Winnaar, who settled in the Matlakeng area in May–June 1838; as more Boers were moving into the area they tried to colonise the land between the two rivers north of the Caledon, claiming that it had been abandoned by the Sotho people.
Moshoeshoe subsequently signed a treaty with the British Governor of the Cape Colony, Sir George Thomas Napier, that annexed the Orange River Sovereignty that many Boers had settled. These outraged Boers were suppressed in a brief skirmish in 1848. In 1851 a British force was defeated by the Basotho army at Kolonyama, touching off an embarrassing war for the British. After repelling another British attack in 1852, Moshoeshoe sent an appeal to the British commander that settled the dispute diplomatically defeated the Batlokoa in 1853. In 1854 the British pulled out of the region, in 1858 Moshoeshoe fought a series of wars with the Boers in the Free State–Basotho War, losing a great portion of the western lowlands; the last war in 1867 ended when Moshoeshoe appealed to Queen Victoria, who agreed to make Basutoland a British protectorate in 1868. In 1869, the British signed a treaty at Aliwal North with the Boers that defined the boundaries of Basutoland, Lesotho, which by ceding the western territories reduced Moshoeshoe's Kingdom to half its previous size.
Following the cession in 1869, the British transferred functions from Moshoeshoe's capital in Thaba Bosiu to a police camp on the northwest border, until administration of Basutoland was transferred to the Cape Colony in 1871. Moshoeshoe died on 11 March 1870, marking the end of the traditional era and the beginning of the colonial era, he was buried at Thaba Bosiu. In the early years of British rule between 1871 and 1884, Basutoland was treated to other territories, forcibly annexed, much to the chagrin of the Basotho; this led to the Gun War in 1881. In 1884, Basutoland was restored to its status as a protectorate, with Maseru again its capital, but remained under direct rule by a governor, though effective internal power was wielded by traditional chiefs. Basutoland gained its independence from Britain and became the Kingdom of Lesotho in 1966. In January 1970, the ruling Basotho National Party lost the first post-independence general elections, with 23 seats to the Basutoland Congress Party's 36.
Prime Minister Leabua Jonathan refused to cede power to the Basotho Congress Party, declared himself Tona Kholo, imprisoned the BCP leadership. BCP began a rebellion and received training in Libya for its Lesotho Liberation Army under the pretense of being Azanian People's Liberation Army soldiers of the Pan Africanist Congress. Deprived of arms and supplies by the Sibeko faction of the PAC in 1978, the 178-strong LLA was rescued from their Tanzanian base by the financial assistance of a Maoist PAC officer, but they launched the guerrilla war with only a handful of old weapons; the main force was defeated in northern Lesotho, guerrillas launched sporadic but ineffectual attacks. The campaign was compromised when BCP's leader, Ntsu Mokhehle, went to Pretoria. In the early 1980s, several Basotho who sympathised with the exiled BCP were threatened with death and attacked by the government of Leabua Jonathan. On 4 September 1981, the family of Benjamin Masilo was attacked. In the attack his 3-year-old grandson lost his life.
Four days Edgar Mahlomola Motuba, the editor of the popular newspaper Leselinyana la Lesotho, was abducted from his home together with two friends and murdered. The BNP ruled from 1966 until January 1970. What ensued was a de facto government led by Dr. Leab
South Africa the Republic of South Africa, is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres of coastline of Southern Africa stretching along the South Atlantic and Indian Oceans. South Africa is the largest country in Southern Africa and the 25th-largest country in the world by land area and, with over 57 million people, is the world's 24th-most populous nation, it is the southernmost country on the mainland of the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different African languages, nine of which have official status; the remaining population consists of Africa's largest communities of European and multiracial ancestry. South Africa is a multiethnic society encompassing a wide variety of cultures and religions, its pluralistic makeup is reflected in the constitution's recognition of 11 official languages, the fourth highest number in the world. Two of these languages are of European origin: Afrikaans developed from Dutch and serves as the first language of most coloured and white South Africans.
The country is one of the few in Africa never to have had a coup d'état, regular elections have been held for a century. However, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a large role in the country's recent history and politics; the National Party imposed apartheid in 1948. After a long and sometimes violent struggle by the African National Congress and other anti-apartheid activists both inside and outside the country, the repeal of discriminatory laws began in 1990. Since 1994, all ethnic and linguistic groups have held political representation in the country's liberal democracy, which comprises a parliamentary republic and nine provinces. South Africa is referred to as the "rainbow nation" to describe the country's multicultural diversity in the wake of apartheid; the World Bank classifies South Africa as an upper-middle-income economy, a newly industrialised country.
Its economy is the second-largest in Africa, the 34th-largest in the world. In terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa; however and inequality remain widespread, with about a quarter of the population unemployed and living on less than US$1.25 a day. South Africa has been identified as a middle power in international affairs, maintains significant regional influence; the name "South Africa" is derived from the country's geographic location at the southern tip of Africa. Upon formation, the country was named the Union of South Africa in English, reflecting its origin from the unification of four separate British colonies. Since 1961, the long form name in English has been the "Republic of South Africa". In Dutch, the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika. Since 1994, the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning "south", is a colloquial name for South Africa, while some Pan-Africanist political parties prefer the term "Azania".
South Africa contains human-fossil sites in the world. Archaeologists have recovered extensive fossil remains from a series of caves in Gauteng Province; the area, a UNESCO World Heritage site, has been branded "the Cradle of Humankind". The sites include one of the richest sites for hominin fossils in the world. Other sites include Gondolin Cave Kromdraai, Coopers Cave and Malapa. Raymond Dart identified the first hominin fossil discovered in Africa, the Taung Child in 1924. Further hominin remains have come from the sites of Makapansgat in Limpopo Province and Florisbad in the Free State Province, Border Cave in KwaZulu-Natal Province, Klasies River Mouth in Eastern Cape Province and Pinnacle Point and Die Kelders Cave in Western Cape Province; these finds suggest that various hominid species existed in South Africa from about three million years ago, starting with Australopithecus africanus. There followed species including Australopithecus sediba, Homo ergaster, Homo erectus, Homo rhodesiensis, Homo helmei, Homo naledi and modern humans.
Modern humans have inhabited Southern Africa for at least 170,000 years. Various researchers have located pebble tools within the Vaal River valley. Settlements of Bantu-speaking peoples, who were iron-using agriculturists and herdsmen, were present south of the Limpopo River by the 4th or 5th century CE, they displaced and absorbed the original Khoisan speakers, the Khoikhoi and San peoples. The Bantu moved south; the earliest ironworks in modern-day KwaZulu-Natal Province are believed to date from around 1050. The southernmost group was the Xhosa people, whose language incorporates certain linguistic traits from the earlier Khoisan people; the Xhosa reached the Great Fish River, in today's Eastern Cape Province. As they migrated, these larger Iron Age populations
An ion is an atom or molecule that has a net electrical charge. Since the charge of the electron is equal and opposite to that of the proton, the net charge of an ion is non-zero due to its total number of electrons being unequal to its total number of protons. A cation is a positively charged ion, with fewer electrons than protons, while an anion is negatively charged, with more electrons than protons; because of their opposite electric charges and anions attract each other and form ionic compounds. Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a medium, such as a gas, "ion pairs" are created by ion collisions, where each generated pair consists of a free electron and a positive ion. Ions are created by chemical interactions, such as the dissolution of a salt in liquids, or by other means, such as passing a direct current through a conducting solution, dissolving an anode via ionization.
The word ion comes from the Greek word ἰόν, ion, "going", the present participle of ἰέναι, ienai, "to go". This term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday did not know the nature of these species, but he knew that since metals dissolved into and entered a solution at one electrode and new metal came forth from a solution at the other electrode; this conveys matter from one place to the other. In correspondence with Faraday, Whewell coined the words anode and cathode, as well as anion and cation as ions that are attracted to the respective electrodes. Svante Arrhenius put forth, in his 1884 dissertation, his explanation of the fact that solid crystalline salts dissociate into paired charged particles when dissolved, for which he would win the 1903 Nobel Prize in Chemistry. Arrhenius' explanation was. Arrhenius proposed that ions formed in the absence of an electric current.
Ions in their gas-like state are reactive and will interact with ions of opposite charge to give neutral molecules or ionic salts. Ions are produced in the liquid or solid state when salts interact with solvents to produce solvated ions, which are more stable, for reasons involving a combination of energy and entropy changes as the ions move away from each other to interact with the liquid; these stabilized species are more found in the environment at low temperatures. A common example is the ions present in seawater; as charged objects, ions are repelled by like charges. When they move, their trajectories can be deflected by a magnetic field. Electrons, due to their smaller mass and thus larger space-filling properties as matter waves, determine the size of atoms and molecules that possess any electrons at all. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other and add to the physical size of the ion, because its size is determined by its electron cloud.
Cations are smaller than the corresponding parent atom or molecule due to the smaller size of the electron cloud. One particular cation contains no electrons, thus consists of a single proton - much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, the net electric charge on an ion is equal to the number of protons in the ion minus the number of electrons. An anion, from the Greek word ἄνω, meaning "up", is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κάτω, meaning "down", is an ion with fewer electrons than protons, giving it a positive charge. There are additional names used for ions with multiple charges. For example, an ion with a −2 charge is known as a dianion and an ion with a +2 charge is known as a dication. A zwitterion is a neutral molecule with positive and negative charges at different locations within that molecule. Cations and anions are measured by their ionic radius and they differ in relative size: "Cations are small, most of them less than 10−10 m in radius.
But most anions are large, as is oxygen. From this fact it is apparent that most of the space of a crystal is occupied by the anion and that the cations fit into the spaces between them."A cation has radius less than 0.8 × 10−10 m while an anion has radius greater than 1.3 × 10−10 m. Ions are ubiquitous in nature and are responsible for diverse phenomena from the luminescence of the Sun to the existence of the Earth's ionosphere. Atoms in their ionic state may have a different colour from neutral atoms, thus light absorption by metal ions gives the colour of gemstones. In both inorganic and organic chemistry, the interaction of water and ions is important; the following sections describe contexts. Ions can be non-chemically prepared using various ion sources involving high voltage or temperature; these are used in a multitude of devices suc
The electron is a subatomic particle, symbol e− or β−, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, are thought to be elementary particles because they have no known components or substructure; the electron has a mass, 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant, ħ; as it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light; the wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy. Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism and thermal conductivity, they participate in gravitational and weak interactions.
Since an electron has charge, it has a surrounding electric field, if that electron is moving relative to an observer, it will generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as electronics, cathode ray tubes, electron microscopes, radiation therapy, gaseous ionization detectors and particle accelerators. Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics; the Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms.
Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge'electron' in 1891, J. J. Thomson and his team of British physicists identified it as a particle in 1897. Electrons can participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere; the antiparticle of the electron is called the positron. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons.
The ancient Greeks noticed. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electrica, to refer to those substances with property similar to that of amber which attract small objects after being rubbed. Both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον. In the early 1700s, Francis Hauksbee and French chemist Charles François du Fay independently discovered what they believed were two kinds of frictional electricity—one generated from rubbing glass, the other from rubbing resin. From this, du Fay theorized that electricity consists of two electrical fluids and resinous, that are separated by friction, that neutralize each other when combined. American scientist Ebenezer Kinnersley also independently reached the same conclusion. A decade Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess or deficit.
He gave them the modern charge nomenclature of negative respectively. Franklin thought of the charge carrier as being positive, but he did not identify which situation was a surplus of the charge carrier, which situation was a deficit. Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges. Beginning in 1846, German physicist William Weber theorized that electricity was composed of positively and negatively charged fluids, their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion, he was able to estimate the value of this elementary charge e by means of Faraday's laws of electrolysis. However, Stoney could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".
Stoney coined the term
Brilliant (diamond cut)
A brilliant is a diamond or other gemstone cut in a particular form with numerous facets so as to have exceptional brilliance. The shape resembles that of a cone and provides maximized light return through the top of the diamond. With modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; the round brilliant cut is preferred when the crystal is an octahedron, as two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to; the original round brilliant-cut was developed by Marcel Tolkowsky in 1919. The modern round brilliant consists of 58 facets, ordinarily today cut in two pyramids placed base to base: 33 on the crown, truncated comparatively near its base by the table, 25 on the pavilion, which has only the apex cut off to form the culet, around which 8 extra facets are sometimes added.
In recent decades, most girdles are faceted. Many girdles have 64, 80, or 96 facets. While the facet count is standard, the actual proportions are not universally agreed upon; some gem cutters refer to a Scandinavian brilliant cut. Quoting Green et al. 2001: Because every facet has the potential to change a light ray's plane of travel, every facet must be considered in any complete calculation of light paths. Just as a two-dimensional slice of a diamond provides incomplete information about the three-dimensional nature of light behavior inside a diamond, this two-dimensional slice provides incomplete information about light behavior outside the diamond. A diamond's panorama is three-dimensional. Although diamonds are symmetrical, light can enter a diamond from many directions and many angles; this factor further highlights the need to reevaluate Tolkowsky's results, to recalculate the effects of a diamond's proportions on its appearance aspects. Another important point to consider is that Tolkowsky did not follow the path of a ray, reflected more than twice in the diamond.
However, we now know that a diamond's appearance is composed of many light paths that reflect more than two times within that diamond. Once again, we can see that Tolkowsky's predictions are helpful in explaining optimal diamond performance, but they are incomplete by today's technological standards. Figures 1 and 2 show the facets of a round brilliant diamond. Figure 1 assumes that the "thick part of the girdle" is the same thickness at all 16 "thick parts", it does not consider the effects of indexed upper girdle facets. Figure 2 is adapted from Figure 37 of Marcel Tolkowsky's Diamond Design, published in 1919. Since 1919, the lower girdle facets have become longer; as a result, the pavilion main facets have become narrower. The relationship between the crown angle and the pavilion angle has the greatest effect on the look of the diamond. A steep pavilion angle can sometimes be complemented by a shallower crown angle, vice versa. Other proportions affect the look of the diamond: The table ratio is significant.
The length of the lower girdle facets affects whether Hearts and arrows can be seen in the stone, under certain viewers. Most round brilliant diamonds have the same girdle thickness at all 16 "thick parts". So-called "cheated" girdles have thicker girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the girdle; these stones weigh more, have worse optical performance. So-called "painted" girdles have thinner girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the girdle; these stones have less light leakage at the edge of the stone. Some diamonds with painted girdles receive lower grades in the GIA's cut grading system, for reasons given in a 2005 GIA article. Several groups have developed diamond cut grading standards, they all disagree somewhat on. There are certain proportions; the AGA standards may be the strictest. David Atlas has suggested; the HCA changed several times between 2001 and 2004. As of 2004, an HCA score below two represented an excellent cut.
The HCA distinguishes between brilliant and fiery cuts. The American Gem Society standards changed in 2005 to better match Tolkowsky's model and Octonus' ray tracing results; the 2005 AGS standards penalize stones with "cheated" girdles. They grade from 0 to 10; the GIA began grading cut on every grading report beginning 2006 based on their comprehensive study of 20,000 proportions with 70,000 observations of 2,000 diamonds. The single descriptive words are as follows: Excellent, Very Good, Good and Poor; the distance from the viewer's eye to the diamond is important. The 2005 AGS cut standards are based on a distance of 25 centimeters; the 2004 HCA cut standards are based on a distance of 40 centimeters. Polish and symmetry are two important aspects of the cut; the polish grade describes the smoothness of the diamond's facets, the symmetry grade refers to alignment of the facets. With