![]() The chemical process, by which patina forms, is called patination, and an artifact coated by patina is said to be patinated. By extension, the word is applied to the discoloured or in-crusted surface of marble, flint, etc. PATINA has probable origin from a Latin word for shallow dish, or ‘ patere’, =to lie open. In geology and geomorphology, the stone patina also refers to a case-hardened layer, called cortex, or corticated layer on the surface of Flint tools or a chert nodule. Wind abrasion removes the softer salts, and polishes the surface to a glossy finish. This is deposition of moisture dissolved minerals drawn to the surface by capillary action of evaporation. Patina also refers to accumulated changes on surface texture and colour, due to long term use of an object like coins or items of wood furniture.ĭesert patina or Varnish is a thin, dark red to black mineral coating (of iron and manganese oxides and silica) seen on exposed pebbles and rocks in desert terrains. Its surface may be smooth, glossy, or crusty. Patinas are commonly green, but may vary in colour such as of r ed, brown, black, blue, or gray colours. Similar effects can be achieved by designed exposure and by treating with various chemicals. Metal artefacts exposed to different environments such air, sea-water, soils acquire patina. Patinas are visually appealing and so desired. Some patinas, however, curtail further degradation of the surface and so are encouraged. Patinas are formed by degradation of the surface mass and so etch or reduce its thickness. Metal patina is a coating formed due to environmental exposure consisting of oxides, carbonates, sulfides, or sulfates. Similar surface layers formed on other metals, stone, pottery, wood, etc. Patina is a thin crust like surface layer forming on Bronze. Many musical instruments’ body are made of brass such as the trombone, tuba, trumpet, cornet, euphonium, horn, etc. Bronze is used for striking instruments like bells, cymbals, and plucking strings for guitar and piano. Bronze exhibits low metal-to-metal friction and so used for spark-erosion.īrass and Bronze, both have good vibration transmission properties. Bronze is used for springs, bearings, bushings, etc. The surface however tarnishes unless coated with lacquer.īrass is used for applications where low friction is required such as locks, gears, bearings, plumbing and electrical applications, doorknobs, ammunition, and valves. It is very ductile and malleable, Dutch metal is used for preparation of imitation gold leaf for gilding. As the zinc content is increased the colour becomes paler. The percentage of copper ranges from 85 to 88, rest being zinc. It withstands atmospheric, steam, and seawater corrosion and is suitable for valves, pump parts, and steam fittings.ĭutch metal is a brass that has colour tone like the gold. It is now used for gears and bearings that are to be subjected to heavy loads and low speeds. Gun metal (G metal) is a bronze, formerly used for ordnance. There are few alloys that have remained consistently relevant. Iron was widely available and was harder than copper or brass. Copper was followed by bronze and than iron. It was treated with material removal processes, like chasing and engraving and shaped by die forging, beating and embossing.Ĭopper was the first metal used by man during the Neolithic Period, or New Stone Age, since 8000 BC. Melted bronze on cooling solidifies and expands slightly, filling up the entire mass of the mould.īrass was preferred for its work-ability. This method of casting are expensive and time consuming, but produced fine edges for shapes) Later, wood dummies or dies were used to create a castable hollow in the sands. Bronze and Brass were cast by the cire perdue, or lost-wax, method. Instead brass or copper, which were malleable, allowed hammering and chasing. It was a brittle and rarely hammered or chased. Brass is however, lighter in colour, whereas, Bronze has warmer, reddish hues.įrom a very early date bronze was chiefly used for casting. More over, the colours of patina ( occurring on ageing-weathering) range from blackish, dark brown to a dark greenish shades. The colour shades of these alloys very similar and ranges from gold to reddish tinge, and yellowish, depending on the proportion of basic alloying constituents. The Zinc and Tin, the distinguishing alloyants were in the form of some co-occurring materials or ores. ![]() They were somewhat aware of the ingredients that caused the qualitative difference, as much as their expertise for the tools and techniques required to work with them.īrass is an alloy of copper with zinc, whereas Bronze is and alloy of copper with tin. They did not bother to differentiate the metals. Early metal workers considered both the metals, of the same family. Bronze and Brass are often visually very difficult to distinguish. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |