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Tumbaga
''Tumbaga'' is the name given by Spanish Conquistadors for a non-specific alloy of gold and copper, and metals composed of these elements. Pieces made of tumbaga were widely found in pre-Columbian Mesoamerica in North America and South America. The term is a borrowing from the Tagalog ''tumbaga''. This came from Malay , meaning 'copper' or 'brass'. It has also been spelled ''tumbago'' in literature. Composition and properties Tumbaga is an alloy composed mostly of gold and copper. It has a significantly lower melting point than gold or copper alone . It is harder than copper, but maintains malleability after being pounded. Tumbaga can be treated with a carboxylic acid, such as oxalic acid, to dissolve copper off the surface. What remains is a shiny layer of nearly pure gold on top of a harder, more durable copper-gold alloy sheet. This process is referred to as depletion gilding. Use and function Tumbaga was widely used by the pre-Columbian cultures of Central and South Ame ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Depletion Gilding
Depletion gilding is a method for producing a layer of nearly pure gold on an object made of gold alloy by removing the other metals from its surface. It is sometimes referred to as a "surface enrichment" process. Process Most gilding methods are additive: they deposit gold that was not there before onto the surface of an object. By contrast, depletion gilding is a subtractive process whereby material is removed to increase the purity of gold that is already present on an object's surface. In depletion gilding, other metals are etched away from the surface of an object composed of a gold alloy by the use of acids or salts, often in combination with heat. Since no gold is added, only an object made of an alloy that already contains gold can be depletion gilded. Depletion gilding relies on the fact that gold is highly resistant to oxidation or corrosion by most common chemicals, whereas many other metals are not. Depletion gilding is most often used to treat alloys of gold with copp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Malleability
Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic deformation, which is reversible upon removing the stress. Ductility is a critical mechanical performance indicator, particularly in applications that require materials to bend, stretch, or deform in other ways without breaking. The extent of ductility can be quantitatively assessed using the percent elongation at break, given by the equation: \% \mathrm= \left ( \frac \right )\times100 where l_ is the length of the material after fracture and l_0 is the original length before testing. This formula helps in quantifying how much a material can stretch under tensile stress before failure, providing key insights into its ductile behavior. Ductility is an important consideration in engineering and manufacturing. It defines a material's suitabil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gold Compounds
Gold compounds are compounds by the element gold (Au). Although gold is the most noble of the noble metals, it still forms many diverse compounds. The oxidation state of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers, thiolates, and organophosphines. Au(I) compounds are typically linear. A good example is , which is the soluble form of gold encountered in mining. The binary gold halides, such as gold(I) chloride, AuCl, form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives. Au(III) (referred to as the auric) is a common oxidation state, and is illustrated by gold(III) chloride, . The gold atom centers in Au(III) complexes, like other d8 compounds, are typically square planar, with chemical bonds that have both covalent and ionic character. Gold(I,III) chloride is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Copper Alloys
Copper alloys are metal Alloy, alloys that have copper as their principal component. They have high resistance against corrosion. Of the large number of different types, the best known traditional types are bronze, where tin is a significant addition, and brass, using zinc instead. Both of these are imprecise terms. Latten is a further term, mostly used for coins with a very high copper content. Today the term ''copper alloy'' tends to be substituted for all of these, especially by museums. Copper deposits are abundant in most parts of the world (globally 70 parts per million), and it has therefore always been a relatively cheap metal. By contrast, tin is relatively rare (2 parts per million), and in Europe and the Mediterranean region, and even in prehistoric times had to be Tin sources and trade during antiquity, traded considerable distances, and was expensive, sometimes virtually unobtainable. Zinc is even more common at 75 parts per million, but is harder to extract from its ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hernán Cortés
Hernán Cortés de Monroy y Pizarro Altamirano, 1st Marquis of the Valley of Oaxaca (December 1485 – December 2, 1547) was a Spanish ''conquistador'' who led an expedition that caused the fall of the Aztec Empire and brought large portions of what is now mainland Mexico under the rule of the King of Castile in the early 16th century. Cortés was part of the generation of Spanish explorers and conquistadors who began the first phase of the Spanish colonization of the Americas. Born in Medellín, Spain, to a family of lesser nobility, Cortés chose to pursue adventure and riches in the New World. He went to Hispaniola and later to Cuba, where he received an ''encomienda'' (the right to the labor of certain subjects). For a short time, he served as ''alcalde'' (magistrate) of the second Spanish town founded on the island. In 1519, he was elected captain of the third expedition to the mainland, which he partly funded. His enmity with the governor of Cuba, Diego Velázquez de Cué ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spaniards
Spaniards, or Spanish people, are a Romance-speaking ethnic group native to the Iberian Peninsula, primarily associated with the modern nation-state of Spain. Genetically and ethnolinguistically, Spaniards belong to the broader Southern and Western European populations, exhibiting a high degree of continuity with other Indo-European-derived ethnic groups in the region. Spain is also home to a diverse array of national and regional identities, shaped by its complex history. These include various languages and dialects, many of which are direct descendants of Latin, the language imposed during Roman rule. Among them, Spanish (also known as Castilian) is the most widely spoken and the only official language across the entire country. Commonly spoken regional languages include, most notably, the sole surviving indigenous language of Iberia, Basque, as well as other Latin-descended Romance languages like Spanish itself, Catalan and Galician. Many populations outside Sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grand Bahama
Grand Bahama is the northernmost of the islands of the Bahamas. It is the third largest island in the Bahamas island chain of approximately 700 islands and 2,400 cays. The island is roughly in area and approximately long west to east and at its widest point north to south. Its westernmost town, West End, is located east of Palm Beach, Florida. Administratively, the island consists of the Freeport Bonded Area and the districts of East Grand Bahama and West Grand Bahama. Nearly half of the homes on the island were damaged or destroyed in early September 2019 by Hurricane Dorian. Climate Grand Bahama Island has a tropical monsoon climate, consisting of a hot, rainy season from May through October, and a warm, dry season from November through April. In Freeport, the summer high temperatures average , and low temperatures average . During the winter, the average high temperature is , and the average low is . The hurricane season lasts from June through November, but the ris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lost-wax Casting
Lost-wax castingalso called investment casting, precision casting, or ''cire perdue'' (; borrowed from French)is the process by which a duplicate sculpture (often a metal, such as silver, gold, brass, or bronze) is cast from an original sculpture. Intricate works can be achieved by this method. The oldest known examples of this technique are approximately 6,500 years old (4550–4450 BC) and attributed to gold artefacts found at Bulgaria's Varna Necropolis. A copper amulet from Mehrgarh, Indus Valley civilization, in present-day Pakistan, is dated to circa 4,000 BC. Cast copper objects, found in the Nahal Mishmar hoard in southern Israel, which belong to the Chalcolithic period (4500–3500 BC), are estimated, from carbon-14 dating, to date to circa 3500 BC. Other examples from somewhat later periods are from Mesopotamia in the third millennium BC. Lost-wax casting was widespread in Europe until the 18th century, when a piece-moulding process came to predominate. The step ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxalic Acid
Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name is derived from early investigators who isolated oxalic acid from flowering plants of the genus '' Oxalis'', commonly known as wood-sorrels. It occurs naturally in many foods. Excessive ingestion of oxalic acid or prolonged skin contact can be dangerous. Oxalic acid is a much stronger acid than acetic acid. It is a reducing agent and its conjugate bases hydrogen oxalate () and oxalate () are chelating agents for metal cations. It is used as a cleaning agent, especially for the removal of rust, because it forms a water-soluble ferric iron complex, the ferrioxalate ion. Oxalic acid typically occurs as the dihydrate with the formula . History The preparation of salts of oxalic acid from plants had been known since at least 1745, when ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carboxylic Acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl group (e.g., alkyl, alkenyl, aryl), or hydrogen, or other groups. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion. Examples and nomenclature Carboxylic acids are commonly identified by their trivial names. They often have the suffix ''-ic acid''. IUPAC-recommended names also exist; in this system, carboxylic acids have an ''-oic acid'' suffix. For example, butyric acid () is butanoic acid by IUPAC guidelines. For nomenclature of complex molecules containing a carboxylic acid, the carboxyl can be considered position one of the parent chain even if there are other substituents, such as 3-chloropropanoic acid. Alternately, it can be named ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Melting Point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilibrium, equilibrium. The melting point of a substance depends on pressure and is usually specified at a Standard temperature and pressure, standard pressure such as 1 Atmosphere (unit), atmosphere or 100 Pascal (unit), kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of substances to Supercooling, supercool, the freezing point can easily appear to be below its actual value. When the "characteristic freezing point" of a substance is determined, in fact, the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice, that is, the #Melting point measurements, melting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
