ALABASTER

Post 275 –by Gautam Shah

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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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THERMAL MANAGEMENT – WINDOWS and INTERIOR SPACES

Post 274 –by Gautam Shah

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Delhi Government Building with upper level Ventilator Windows for thermal management

Thermal management by WINDOW VENTILATION

Ventilation affects the heat level of an interior space, by addition, extraction or conservation. The heat exchange is managed by opening-closing of various sections of the window. Openings must be opened prudently, remain open or closed permanently. By scheduling (time or season), and by controlling the extent of opening, heat can be conserved or diffused in the building.

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Thermal management by WINDOW DESIGN

The structure of the opening system is a thin body and so heat transfer through it is far quicker, then with any other component of the building. Thermal performance of a window is a function of three elements: glazing, frame and perimeter details.

Window Twins Prague

Thermal management by WINDOW DESIGN > GLAZING

Glazing is transparent to translucent material that allows transmission of heat across it. Its thin wall has low thermal insulation capacity. But glazing systems with multiple layers, cavity and modern e-coatings show improved thermal performance. Windows with lower U-factors or higher R-values perform better in colder climates, and windows with lower solar heat gain coefficients (SHGC) perform better in warmer climates.

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Thermal management by WINDOW DESIGN >LOW-E COATINGS

Low-e coatings minimize the amount of ultraviolet and infrared light that can pass through glass without compromising the amount of visible light that is transmitted. It reflects long-wave infrared energy or heat and significant amounts of short-wave solar infrared energy. When during the winter, interior heat energy that tries to escape colder outside, the low-e coating reflects the heat back to interior space, reducing the radiant heat loss. A reverse process occurs during warmer days. Low-e coatings are applied directly on the glass or as coated plastic film. Such coatings are inevitable part of the multi layered double / triple glass glazing units. Here Low-e coatings are applied to one glazing surface facing the air gap of the insulating gas unit.

Reflective Glass Building Chicago

Thermal management by WINDOW DESIGN > REFLECTIVE COATINGS

Reflective particles deposited on glazing materials of clear, tinted, or otherwise treated varieties. They generally reduce visible-light transmission, but are less effective for curtailing infrared radiation. Like mirrored glazing, they cause annoying reflection over neighbours’ buildings, which often causing a heat build up there. Frit is the most common angle-selective coating. It consists of a ceramic coating, either translucent or opaque, which is screen-printed in small patterns on a glass surface. The pattern used on the glass controls the light based on its angle of the incidence. The colour of Frit controls the reflection or absorption and the control of view or visual privacy. Visual transparency can also be controlled by applying Frit to both sides of the glass so that at some angles it appears transparent, and at other angles it appears opaque.

Frit Glass

Thermal management by WINDOW DESIGN > DIRECTIONALLY SELECTIVE MATERIALS

Directionally selective materials reject or redirect incident solar radiation based on a geometric relationship between the radiation and material. Such glazing can redirect light to a predetermined location. They include glass blocks, silk-screened glazing, prismatic devices, enclosed louvres, holographic films, and embedded structures.

Paris Glass Building Reflections Facade

Thermal management by WINDOW DESIGN >DYNAMIC GLAZING

Dynamic glazing is called switchable optical windows or smart windows, because the photo-chromatic properties of the glazing can be altered with change in level of illumination or by an electric current. Dynamic glazing also includes polarized glazing materials, which with a change in its inclination curtail view and light (as in rear view mirrors of automobiles). Switchable materials can provide glare reduction, privacy, daylight and solar control, and reduction of ultraviolet transmission.

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Thermal management by WINDOW DESIGN > FRAMES OF THE WINDOW

The frame of the window, its materials, geometry and method of fabrication (e.g. thermal breaks in metal frames), determine thermal behaviour of the opening system. Low conductance materials, such as wood, vinyl, and fibre glass, perform better than high conductance materials such as aluminium or mild steel. Perimeter details of commercial or low-cost windows are extremely poor and have high thermal leakage across joints. High end windows have rubber gaskets, polyurethane fill-in and other thermal breaks (layers of insulation materials that isolates the internal and external surfaces / components). These need to be continuously checked and replaced. Proper placement of insulation material in the voids at the window perimeter and maintaining continuity of the air barrier reduces drafts and energy loss around windows. It is not possible to separate the inside and outside faces of a window completely, as the frame and shutter each are of single body construction. A complete thermal isolation can be best achieved by having two sets of windows placed as non touching entities.

640px-Fenster_-_DreifachverglasungThermal management by WINDOW DESIGN > JOINT DESIGN

Windows are multi component systems with many joints which cause leakage of energy. Windows are now tested and rated for air tightness. A rating, of 0.2 cfm/ft (cubic feet per minute of air leakage per linear foot of window edge) or lower, is considered good. A good window has a rating of 0.1 cfm/ft or lower. Windows with low-emission and solar control coatings, low-conductance gas fills, improved thermal breaks and edge spacers, and better edge sealing techniques cannot be taken granted for the thermal performance. The manner of fixing at the site can alter the thermal behaviour of the window. A window well made and properly fixed at the site still needs to be periodically maintained, as the thermal breaks have a very short life cycle (requiring frequent replacement).

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Thermal management by SHADING DEVICES

These are designed to take optimum advantage of seasonal orientation of solar incidences. The solar gain occurs primarily in reference to the plane of the window, so an alternate method could be to have a variable plane of the window, but that may be architectural style-wise, not a very viable option. However, external shading devices keep the glazing surface in shade, while cutting off the direct solar radiation. Shading devices such as Venetian blinds or vertical louvres are not very effective on the internal face of the opening, as the solar gain has already been admitted into the interior space. But interior shading devices offer glare control, and visual comfort.

O Niemeyer building with shading devices

Thermal Management by SPACE PLANNING AND SCHEDULING

Space planning and scheduling of tasks, are the occupants’ only recourse for thermal management in ready to use spaces. These are required in rigid architectural planning where all faces of building are identical or space units can be sited to just any orientation. As a way out new occupants reset and reschedule their life, to match the available openings related climatic facilities. This is not an easy solution to implement Interior Design intervention for the occupant or their interior design expert.

Shading by siting and scheduling -Kutchh Gujarat India

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ARCHITECTURAL WINDOWS and MECHANICS of VISION

Post 248 – by Gautam Shah

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Architectural windows have many sizes, shapes, form and locations. Wherever and for whatever intentions a window is placed, its most fascinating function is view out, and for some cases the view in. Wherever there is a little crack or opening in a wall like structure, one wants to discover the realm on the other side. Windows, enlarged or small in size, transgressed out and inward, pushed to the floor or roof, to regulate the scope of vision.

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The mechanics of vision depend on several factors, such as: distances of the window frame, vision cone and the frame extent, sill level, lintel level, shading devices, size of window sides, window design or configuration, quality of glazing, level of maintenance, the differences of outside and inside illumination, amount of the glare, treatments on internal and external faces, quality of external surroundings, tasks, orientation, climatic conditions, lighting conditions, need for protection and privacy, etc.

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The notion of the ‘eyes as the window to the psyche’ goes back at least to a text by philosopher Sextus Empiricus (2nd C AD).

The factors regulating the vision continue to evolve with new forms of openings, shutter systems and glazing technologies. A window is a frame, marking the edges of the aperture, and also the reference plane for the visual experience. The frame of a window reflects its structural dependence, but also aspirations for the structural un-susceptibility. The frame is not the body of a window, but rather the sized sides of the openings. The openings’ sides, sill tops and lintel or arched bottoms, in heavier wall structures imposed their presence, with the differential colour tone of the reflected light. These were, both, enhanced or dissolved with techniques like chamfering of sides, placing the window on an extreme inner or outer edge, texturing the side with flutes and carvings. The treatments to the sides affected the framing clarity of the vision.

Residence Abbey Church Holyrood Palace Holyroodhouse

The sides of the openings were encroached or enhanced by additional architectonic elements, such Jambs, sides, entablatures, architraves, pilasters, half columns, pediments, etc. These elements were intended to mould the appearance of the openings, but in many instances undulated the edges of the visual framing.

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Glass windows have been prominent in domestic buildings since the 15th C, before, that these were employed in Gothic churches and public buildings. The Gothic windows were meant for the colourful effect, and due to a high plinth (sills were usually beyond the head level on ground floors) less for vision purposes. Compared to it, the Indian temples have remained without glazing, offer very little for vision-in, though vision out was through an axially placed opening.

High Plinth Windows Tall sill levels Gloucester Cathedral https://www.flickr.com/photos/ell-r-brown/14888694202

Sections of the windows cause stratification of the view. Windows show views in three references: The higher view (above the horizontal eye level or head level), the middle view (within the nominal cone of vision) and the lower view (eye and the head both bend downward). The stratification of view becomes obvious when working some distance away (typically equal to one human height measure) from the window. A person working close to the face of a window may get all three views from a mid level opening. The strata are more pronounced in windows with horizontal baffles as the shading component.

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Stratification of View by Window divisions

Higher view from the upper section of a multi-story building shows up only sky, a very static view. But higher view in a low rise building shows upper parts of surrounding buildings, mid portions of trees, and horizon, a slightly changing view, but not strong enough to cause any distraction. Mid level views on busy streets, are distracting due to continuously moving objects outside, and varying illumination and reflections in the interior space. Mid level views from any floor are ergonomically not exerting for most tasks. Low level view from upper floors show up the grounds, gardens, lower terraces, water bodies, etc. All of these surfaces very strongly reflect the changes in solar illumination, shadows, moving objects, etc. The ceiling surfaces become extremely vivid due to the upward reflections, not an ideal proposition for bed rooms, rest rooms and hospital wards.

Corner window

A fully stretched floor to ceiling window shows all the three views concurrently, and as a result there is no stratification of the view. The strata can be supported or diffused, by including or avoiding the horizontal elements in window design.

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Open Zarokhas, bay windows and Latticed balconies, like at the Jaipur Hawa Mahal or Mashrabiya of middle east, are two opposite versions of street side openings.

Mashrabiya Egypt

Historically, windows have not been used for viewing in the interior spaces. Though small aperture openings, alone or as part of the doors, were used for eavesdropping, spying or casual observation (Darshan). These were small sized because the eye was placed very close to the aperture. Display cabinets and Aquariums have glazed fronts to display the items. Office and cabin doors have view windows.

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Commercial spaces require people to see the interiors’ spaces and the goods and activities therein. Shop fronts are large format fixed glass windows. A shop front design depends on the angle of observation, difference between outside-inside illumination, angles of a light source, its size and intensity. Shop fronts are designed for clear and glare free view, achieved by treatments over glass, external shading devices and through back up illumination. The quality of glass and its cleanliness become very important issue. A view-in window like the shop front ensures security as a person breaking-in is likely to be observed.

Glass store-fronts

The cone of vision is determined by the width of the window and depth of the room. A corner side window cuts off the view compared to a centrally positioned window. Ribbon like horizontal windows are called panoramic openings, whereas spot windows are called picture openings.

Villa Savoye Ribbon window

Panoramic views became popular with curtain wall structures. Here the horizontal members are placed floor level, and verticals are widely spaced or concealed. The glass walled window has the R-value of 3, which is the same as an inch of corrugated cardboard, making it a space of uneven temperatures. A study by the Urban Green Council, says that 59% of New Yorkers keep the blinds closed over their big glass windows.

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The excitement of the frontal panoramic view and domed eye view of Pantheon have gone a step further. It started with Caboose rail wagons, where a dome projection over the roof allowed all round vision. The view down is being tried in many different formats. Sears Tower in Chicago has installed four glass box viewing platforms or sky-deck (called Deck) that juts out 1.2 mt, at 103 floors level.

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The television screen as a replacement of a traditional window, creates ‘spatial ambiguity between public and private space’. In German post-war-architecture, the transparency of glass was equated with the transparency of the democratic government (dome of the former Reichstag in Berlin).

Glass Box Balcony 1

Glass Box Balcony 2

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ARCHITECTURAL WINDOWS and VISION IN – OUT

 

Post 247 – by Gautam Shah

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For ages, seeing is implied in the word window,  such as in auga = eye ( ‘vindauga’ mean a ‘wind eye’). It was replaced in old English eagþyrl, (eye-hole), and eagduru (eye-door).

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Walls of a building demarcate two distinctive worlds of inside and outside, but walls being opaque only, one is experienced at a time, and the other is unseen, so ignored. Openings like doors and windows allow the connection between the two realms to be simultaneously live. The see-through unglazed or glazed opening allows a chance for deliberation, which in case of a window is less causative then a door. The door threshold, real or imaginary can be transgressed either way at will, but a window sill is not always trespass-able from outside. Few windows have known or hospitable terrain outside. Only thing that could come through a middle age backyard window was the stench of the garbage or the night-soil thrown out every day. The backyard window, facing mass of buildings had little to offer as a view, but replacing the louvres with a pane of glass did stop the stench.

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The gaze in or out of a window, for many years, was not considered a great problem, as the casting-forming defects in the glass (and earlier mica or alabaster), made it fuzzy. The glass panes for the windows, even though muddled, were rare, costly and fragile. The cost and bother of their replacement was a major matter. The glass size was small, so needed framing by several muntins and mullions, making the entire glazed opening prone to sagging. Glazed openings were mainly used in public buildings or for rich mansions. These were the people who could afford frequent glass replacement, and when technology offered, replace it with clearer quality of glass.

 

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15th C architect, sculptor, painter, and theorist Leon Battista Alberti, considered a painting to resemble a view out of a window. ‘First of all, on the surface on which I am going to paint, I draw a rectangle of whatever size I want, which I regard as an open window through which the subject to be painted is seen;…’ . Alberti formulated the method of one-point linear perspective for scene painting. The window frame defined the canvas to scale, form the depth as a meta screen.

Dürer’s woodcut shows metaphoric use of window as a glass screen for forming one point perspective.

This intimate connection of seeing, outside, airiness, of windows transforms into metaphoric perception, realization and ultimately to the soul. The tunnel end is an opening of relief, so is a window that manifests where none was expected. It is like a dream that is remembered on sudden opening of the eye. An opaque window is called a blind opening, and set of louvered slats are window blinds. All early versions of the Televisions and Computers had a very strong window frame and were called windows to the world. Radio remained without a frame, just a listening device. These similes somehow show a window to be switch-able, open and shut case (a simple and straightforward situation without complications). The curtain masking, film layering and metallizing of the glass are concealing what is on the inside.

Framed TV screen like window

Frame-less Screen

In early Gothic buildings the day and night visions of the buildings were completely different. During daytime the interiors were brilliantly filled with colour, but the exterior face presented dull, almost flat, grey face of the glass, with very little perception of the colours of the stained glass. During night time, in the beginning phase, the building was even duller. But soon it began to be lit on inside by oil lamps and candles. Now the building on the outside had a colourful glow against the dark -street-lights less city scape. The glass became lighter coloured (Grisaille) and staining only selective, The oil lamps and candles, in large numbers, a created maintenance problem of soot removal. Private mansions began to have towers topped with a glass cage lit at night.

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Stained Glass during daytime from outside

In the post Industrial revolution period the window became free of the wall as curtain wall, providing uninterrupted view in commercial buildings. Mies van der Rohe did the same thing for a dwelling in Farnsworth House. Le Corbusier in earlier phase used the glass as a grey surface, but in a later phase the glass becomes an unimportant feature, on the outside masked by architectonic elements like brise de soleil.

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Fransworth House

Windows for transactions in Banks, Post offices and Government departments were once pigeon holes in opaque walls, not allowing much visual exchange. This became glass fronts with pigeons’ holes, encouraging a visual exchange, later became across the table relationship, and now remote and internet connection. The window form has also turned from a little hole to a large glass pane wall, and behind a screen or communication window.

Fixing Metallic Transparency Glass Front Metal

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GLASS in WINDOWS – Part • I

Post 198 –by Gautam Shah

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The window like its counterpart the door was a solid shuttered opening in clod climates and a latticed one in warm climates. It did not offer any other options. The first alternative was provided by the soft covering like a curtain. It offered translucency of diffused light and privacy, but did not protect the interior from high winds, rains or cold.

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512px-Village_window_in_T_gollarahatti,a_village_near_channagiri,davenagereThe first glass in an opening was the little cast disk fixed in the roofs. The disks were cast in sand shallow pits, and partially ground to improve its translucency. Technologically it was not possible to produce larger disks and of better transparency. Other materials for window covering were leather (as parchment), wax or oil coated woven clothes, thin pieces of alabaster, and in the orients -the paper.

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The first window glass ‘panes’ began to be produced after 1st C AD. These were sheets flattened out of blown glass jars or bottles. Two types of glass were flattened, one was the bottom disc and the other was the cylindrical wall of the blown form. Both, however, retained some curvature of the body, and had poor quality. The poor quality resulted from the inferior glass production technology, retention of curvilinear patterns, poor flattening surface, and poor annealing technology (to remove stresses to make it less brittle). Small size and its slightly curved shape made fixing very difficult.

First commercially (16-17C) produced windows glass was broad cylinder sheet. It was known as broad or muff glass. It was formed by cutting a blown glass cylinder sideways and flattening on a table when still hot. It had uneven thickness, lines marks, and was stuck with dust, sand particles, air bubbles. It was produced till 18 C but the process remained in use till 19 C due to its low requirement of technology. Crown Glass which replaced the cylinder glass, was a flattened bottom disk of a blown glass bulb. It was to an extent was clearer. It had high lustre and lesser stuck-on impurities. It had though unique concentric rings.

Bhutan Houses show many of the ancient usage of glass

Bhutan Houses show many of the ancient usage of glass

Large openings were sub-divisioned by mullions of wood, stone or metals. But technologically the glass was not large enough to cover the inter-mullion space. So small pieces of glass were joined by lead, and very occasionally with crude mastic compound of bitumen. The lead joints and mullions both were used to form patterns. The mullions were of stiffer materials, so formed little stiffer or geometric patterns whereas the lead was soft option amenable to floral and artistic linear patterning. The third option, now added, was to exploit glass casting figures, tinge variations, and manufacturing ‘defects’ as colour-texture-transparency variations.

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The window in spite of its static form and glass limitations was a very lively interior surface. The builder also realized the importance of quality of light on various orientations. The windows were devised in consideration of the quality of light from various directions, the scheduling of activities within the building, its profile and location (chamfered inside-outside, low level or clerestory). The nature of Interior treatments, such as paintings (fresco, gesso, etc.), murals (marble, glass mosaic, etc.), gilding, wood work, stone cladding, engraved surfacing, etc. were all affected by the quality of glass in the window, and in turn affected the type of glass being used in the windows.

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