ALABASTER

Post 275 –by Gautam Shah

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Amber_Palace-Sukh_Mandir-Alabaster_decor

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Alabaster has been used for decorative objects since 3500BC. It is believed that one of the sources for Alabaster was Alabastron, a town in Egypt. The Greek mineral name alabastrites is derived from that town. The word alabaster relates to Greek –alabastros or alabastos, and old French –alabastre. Alabaster also connects to ancient Egyptian word a-labaste that refers to vessels of the Egyptian Goddess Bast.

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‘Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. When conditions are right for dissolution, the removal of calcite can dramatically increase the porosity and permeability of the rock, and if it continues for a long period of time may result in the formation of caves. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, resulting in various forms of karst topography’. (from Wikipedia).

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640px-Alabaster_Bazylika_JGAlabaster is translucent whitish kind of gypsum. It is a soft and easy to work or carve material used for making vases, ornaments, bottles, jars, busts and ornamental objects. A three-foot vase with a relief from Warka, of 3500-3000 BC (in British Museum), busts from Sumer, of 3000 BC (Louvre), ornate triple lotus oil lamps found in the Tomb of Tutankhamen 1356 BC, and Sarcophagus of Seti I 1304 BC, are some ancient items made of alabaster. Decorative artefacts of Alabaster have been found in Sumer, Babylonia, Assyria and Roman empire. In later periods it was used in India from 6th to 13th C.

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Ancient Egypt alabaster vessels Florence

Alabaster are broadly two classes of minerals, a sulphate of lime or a pure variety of gypsum, and the other is a carbonate of lime, akin to a marble in composition. Due to the close resemblance of the two materials, in terms colour and grain, some ambiguity in distinct identification has persisted. The gypsum alabaster or the oriental alabaster is more softer, delicate and needs care in polishing. It soon tarnishes on atmospheric exposure, and affected by dust and smoke. The carbonate alabaster is little more firmer and so more suitable for larger items. This was sourced from caves where lime water drips to form natural deposits or moulded forms. It is also called onyx-marble or alabaster-onyx, or simply as onyx. There are several types of alabaster found, including pink, white, and black.

Pietà, 1440, Alabaster, Museum Frankfurt

600px-Norbury,_Derbyshire_-_Nicholas_FitzherbertAlabaster have been modified by various treatments. To make it opaque like a marble, its translucency is reduced by immersing the completed work in a bath of water, and gradually heating, so that stone does not become dead white or chalky. The treated material is called marmo-di-Castellina. Alabaster is also tinted to accentuate the natural veins or to add colour that matches the stone or wood in the surroundings. This is done to produce make-believe coral for decorative elements like rails of staircases, handles and trims.

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Lioness_Bast_cosmetic_jar_83d40m_tut_burial_artifactAlabaster was used as translucent panels before the advent of glass, in openings of monasteries in Mediterranean countries, like Greece, France, Italy and Spain. Alabaster cut into thin sheets is translucent enough for dull interior illumination.

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Inspired by dull glow of Alabaster panels, Thin Marble panels have been used as exterior wall units for Beinecke Rare Book & Manuscript Library Yale University in New Haven, Connecticut. Large alabaster sheets have been used extensively in a Contemporary Cathedral of Our Lady of the Angels, 2002 AD, The cathedral incorporates special cooling system to prevent the panes from overheating and turning opaque.

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SHEER FABRICS and CURTAINS

SHEER FABRICS and CURTAINS

Post 242 ⇒   by Gautam Shah 

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A Sheer fabric is made from very thin threads and low density construction through knitting or weaving. The threads are of Silk, Cotton, Rayon, Nylon and Polyester synthetics. Silk and Cotton are short staple fibres and provide a dull finish, whereas Rayons have little sheen, but most polyesters are filaments (very long fibres) create a glossy finish. The density of a fabric (knitted or woven) determined by several factors such as sectional form the fibre, degree of spinning, massing during spinning and weaving (measured as Denier). The resultant fabrics are transparent, translucent or opaque.

Sheer fabric dress

DENIER: A Denier is a unit of measurement for fineness of fibres or filaments, as threads, expressed as the weight in grams for 9,000 metres length of yarn. The surface area of a fabric is directly related to the denier. Smaller deniers yield more fibres per unit weight of the material.

A micro-fiber is less than 1 denier, fibres for sheer fabrics are finer, just 0.9 denier, in comparison, a human hair is 20 denier. The sheerness of a fabric is expressed in denier, 3-5 is extremely thin, barely visible like clear film, 15 to 40 are used in making stockings, and 100 is fairly opaque.

COUNT: Fabrics’ coarseness or fineness, produced by weaving or knitting, are measured in threads counts (both-way) per unit area, (and also warp-ends per inch e.p.i, and weft-picks per inch p.p.i.).

Silk Sheer

Fabrics with a high denier measure tend to be thick, sturdy, and durable, whereas fabrics with a low denier measure tend to be sheer, soft, and smooth. Sheer fabrics are used as curtains on external face and as dividers in interior spaces. Sheer fabrics, however, are too thin to control incoming sunlight. Sheer curtains filter light, and cause its de-fraction.

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In the post middle ages period, glass for windows was flattened from cylindrical form or flat cast. Flattened glass had crinkles and cast one unevenly polished. It was available in small pieces, and even then vision through it was distorted, muddled or frosty. The sheer curtain masked the vision through the window, and provided visual privacy. Sheer curtain fabrics do not offer any insulation against heat or cold, so need additional cover of heavy-opaque fabric curtains. Sheer curtains over bedsteads provide a romantic transparency, provided room is heated (or air conditioned). Sheer fabrics of low denier and high count weaves have little sound absorption, but higher proportion of gathers or creases substantial add to sound insulation capacity.

Dyed Silk Yarn -greater Opacity

Sheer fabrics of natural fibres such as Silk, have yarns with multiple fibre stands, whereas Cotton has several staples entwined during spinning, both of these create a fabric that is dull or with little sheen. Rayons are produced as staples so have a slight sheen, unless treated differently. Synthetic fibres such as Nylon and Polyesters are in filaments or very long staples and usually with same cross sectional shape, so provide slightly glossy face. Denser weaves have more sheen or shine. Sheer fabrics of netting type have comparatively low gloss due to greater de-fraction of light.

Preferred sheer fabrics are whites, white, natural (un-dyed) shades of white or off-whites, cream, ivory, colour shades. Though many base shades and prints are available. Lighter colours are preferred, due to the greater capacity to de-fract the light. Colour tinted sheer fabrics were popular to tinge the room with a particular hue with natural illumination through the windows. That is no longer needed as vast varieties of paints and wall finishes with subtle variations of hues are available.

Sheer -transparency and illumination

SILK

Silk has been the choice fabric for sheer curtains, for people who can afford it. Silk yarns are made of several very fine long staples or filaments, which give strength, dullness and a natural suppleness. Silk has one the most gracious fall of all sheer fabrics. Silk fabrics are thin, but often sized to add body to it. Heavy bodying, treatments and heavy deniers of fibres and counts of weaving, make a silk fabric opaque. Such opaque fabrics though miss some of the grace in fall, are still liked for curtain making.

Art Silk or artificial silks are made by treating polyester fibres, or by co-spinning the filament with rayon, cotton and silk staples. The main purpose of increasing suppleness is achieved by treatments and mix design, whereas fall is achieved by thin or low density weaving.

Synthetic sheer fabric

Sheer fabrics must not be used with a lining fabric to maintain its translucency and climate-related behaviour. Sheer fabrics are also embellished and embroidered for patterns. Such extra work only adds to the weight of the fabric at the cost of graceful fall. Sheer fabrics are commonly heavily pleated and so the total quantity of cloth required is little more then a curtain of regular fabric.

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# Next article in the series deals with Non-Silk Sheer Curtain fabrics

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