National Building Code (NBC)

The National Building Code is a single document in which, like a network, the information contained in various Indian Standards is woven into a pattern of continuity and cogency with the interdependent requirement of sections carefully analyzed and fitted in to make the whole document a cogent continuous volume. A continuous thread of preplanning is woven which, in itself, contributes considerably to the economies in construction particularly in building and plumbing services.

Building codes exist to protect the public’s health, safety and welfare. National Building Codes (NBC) regulate building construction & building use in order to protect the health, safety & welfare of the occupant. You must always take the correct precautionary measures to assure the safety of your family members.

Beginning and history of National Building Code

A Planning Commission was entrusted with the preparation of the National Building Code. For fulfilling this task a Guiding Committee for the preparation of the Code was set up by the Civil Engineering Division Council in 1967. This Committee, in turn, set up 18 specialist panels to prepare the various parts of the Code. The Guiding Committee and its panels comprised of architects, town planners, materials experts, structural, construction, and electrical illumination, air conditioning, acoustics and public health engineers. These experts were drawn from the Central and State Governments, local bodies, professional institutions and private agencies.

First Version - 1970

The first version of the Code was published in 1970. After the National Building Code was published in 1970, a vigorous implementation drive was launched by the ISI to propagate the content and use of the Code among all concerned in the field of planning, designing and construction activities. For this, State-wise implementation conferences were organized with the participation of the leading engineers, architects, town planners, administrators, building material manufacturers, building and plumbing services installation agencies, contractors, etc.

Second version - 1983

The Code, published in 1970 at the instance of planning commission was then revised in 1983. Thereafter three major amendments were issued, two in 1987 and the third in 1997. The 1970 and 1983 versions of the code were recommendatory in nature.

List of Standards along with National Building Code of India 1983

The following list records those standards, which are acceptable as `good practice`, and `accepted standards` in the fulfillment of the requirements of the Code. The latest version of a standard shall be adopted at the time of enforcement of the Code. The standards listed may be used by the Authority as a guide in conformance with the requirements of the referred clauses in the Code.

In the following list the number appearing in the first column within parentheses indicates the number of the reference in this Part.

1. IS: 8888-1978 Guide for requirements of low income housing


2. IS: 6313 Code of practice for anti-termite measures in buildings: IS: 6313 (Part I)-1971 Part I Constructional measures IS: 6313 (Part II)-1971 Part II Pre-constructional chemical treatment measures IS: 6313 (Part III)-1971 Part III Treatment for existing buildings


3. IS: 3792-1978 Guide for heat insulation of non-industrial buildings (first revision)


4. IS: 1634-1973 Code of practice for design and construction of wood stairs in houses (first version)


5. IS: 4838 Anthropometrics dimensions for school children: IS: 4838 (Part I) - 1969 Part I Age group 5 to 11 years IS: 4838 (Part II) - 1969 Part II Age group 12 to 16 years


6. IS: 4963-1968 Recommendations for buildings and facilities for the physically handicapped.

Third version -2005

Considering a series of further developments in the field of building construction including the lessons learnt in the aftermath of number of natural calamities. As a culmination of the Project, the revised NBC has now been brought out as National Building Code of India 2005 (NBC 2005)on 16th September 2005.

It is the third revision compiled under the aegis of the Bureau of Indian Standards (BIS). It provides guidelines for regulating building construction activities across the country. The NBC 2005, formulated by the Bureau of Indian Standards, spells out new regulations for adoption by infrastructure departments, municipal administrators, public bodies and private agencies. It contains mainly administrative regulations, development control rules and general building requirements, fire safety requirements, stipulations on use of materials, structural design and construction and building and plumbing services.

It has the basic codes for construction materials, services, systems and processes. The NBC lays down the minimum provisions buildings need in order to ensure public safety with regard to structural sufficiency, fire hazard and health aspects. It contains administrative provisions, development control rules and general building requirements.

NBC 2005, in addition to the technical specifications for buildings, has for the first time, focussed on the techno-legal requirements, including the scope of participation of professionals in providing the built environment and also pinning responsibility on professionals for the structures that they create.

What’s new in NBC 2005?

It allows architects and engineers to sanction building plans for smaller plots and less complicated structures. It makes it mandatory for architects and structural engineers to take responsibility for the safety of their structure in case of a natural disaster. It provides for a periodic renewal of certificate for occupied buildings from a structural, fire and electrical safety point of view.

The code has detailed town planning norms for amenities such as educational and medical facilities, fire services, etc. It has revised parking requirements for metro and mega cities. Provisions for buildings and facilities for the physically challenged have been revised.

Contents of NBC 2005

Part – 0: Integrated Approach – Prerequisite for Applying Provision of the Code

This part covers guidelines to be followed for judicious implementation of the provisions of various parts/sections of the Code.

Part – 1: Definitions

It lists the terms appearing in all the parts/sections of the National Building Code of India. However, some common definitions are reproduced in this part also.

Part – 2: Administration

It covers the administrative aspects of the Code, such as applicability of the Code, organization of building department for enforcement of the Code, procedure for obtaining development and building permits, and responsibility of the owner and all professionals involved in the planning, design and construction of the building.

Part – 3: Development Control Rules and General Building Requirements

It covers the development control rules and general building requirements for proper planning and design at the layout and building level to ensure health safety, public safety and desired quality of life. It provides provisions for covered area, plinth area, FAR, amenities, land use classification, height/ size of rooms, kitchens etc.

Part – 4: Fire and Life Safety

It covers the requirements for fire prevention, life safety in relation to fire, and fire protection of buildings. The code specifies planning and construction features and fire protection features for all occupancies that are necessary to minimize danger to life and property.

The code cagorises the buildings as follows:

Group A - Residential

Group B - Educational

Group C - Institutional

Group D - Assembly

Group E - Business

Group F - Mercantile

Group G - Industrial

Group H - Storage

Group J - Hazardous

Part -5: Building Material

It covers the requirements of building materials and components, and criteria for accepting new or alternative building materials and components.

29 Materials/ components which have been covered in this part are:

Aluminum & other light materials & their alloys, Bitumen & Tar products, Builders hardware, Building chemicals, Building lime and products, Burnt clay products, Cement & concrete (i/c reinforcement), Composite matrix products, Conductors & cables, Doors / windows & ventilators, Electrical wiring & accessories, Fillers, stoppers & putties, Floor coverings, roofing’s & other finishes, Glass, Gypsum based materials, Lignocellulosic building materials (timber bamboos etc.), Paints & allied products, Polymers, plastics, Sanitary appliances & water fittings, Soil based blocks, Steel & its alloys, Stones, Structural sections, Thermal insulation material, Threaded fasteners & rivets, Unit weight of building materials, Water proofing & damp proofing materials, Welding electrodes & wires, Wire ropes & wire products

Part – 6: Structural Design

This part through its seven sections provides for structural adequacy of buildings to deal with both internal and external environment, and provide guidance to engineers/ structural engineers for varied usage of material / technology types for building design.

Section 1: Loads, Forces and Effects

It covers basic design loads to be assumed in the design of buildings. The live loads, wind loads, seismic loads, snow loads and other loads, which are specified herein, are minimum working loads which should be taken into consideration for purposes of design.

Section 2: Soils and Foundations

It covers structural design (principles) of all building foundations such as raft, pile and other foundation systems to ensure safety and serviceability without exceeding the permissible stresses of the materials of foundations and the bearing capacity of the supporting soil.

Section 3A: Timber

It covers the use of structural timber in structures or elements of structures connected together by fasteners/ fastening techniques.

Section 3B: Bamboo

It covers the use of bamboo for constructional purposes in structures or elements of the structure, ensuring quality and effectiveness of design and construction using bamboo. It covers minimum strength data, dimensional and grading requirements, seasoning, preservative treatment, design and jointing techniques with bamboo which would facilitate scientific application and long-term performance of structures. It also covers guidelines so as to ensure proper procurement, storage, precautions and design limitations on bamboo.

Section 4: Masonry

It covers the structural design aspects of unreinforced load bearing and non-load bearing walls, constructed using various bricks, stones and blocks permitted in accordance with this section. This, however, also covers provisions for design of reinforced brick and reinforced brick concrete floors and roofs.

Section 5A: Plain and Reinforced Concrete

It covers the general structural use of plain and reinforced concrete.

Section 5B: Prestressed Concrete

It covers the general structural use of prestressed concrete. It covers both work carried out on site and the manufacture of precast prestressed concrete units.

Section 6: Steel

It covers the use of structural steel in general building construction including the use of hot rolled steel sections and steel tubes.

Section 7: Prefabrication and Systems Building

Section 7A: Prefabricated Concrete

Though desirable for large scale building activities, has yet to take a firm hold in the country. It includes a few recommendations on the need to avoid ‘progressive collapse’ of the structures.

Section 7B: Systems Building and mixed/ Composite Construction

It covers recommendations regarding modular planning, component sizes, joints, manufacture, storage, transport and erection of prefabricated elements for use in buildings and such related requirements for mixed/composite construction.

Part – 7: Constructional Practices and safety

It covers the constructional practices in buildings; storage, stacking and handling of materials and safety of personnel during construction operations for all elements of a building and demolition of buildings. The objective can be best achieved through proper coordination and working by the project management and construction management teams.

Part – 8: Building Services

This part through its five elaborate sections on utilities provides detailed guidance to concerned professionals/ utility engineers for meeting necessary functional requirements in buildings.

Section 1: Lighting and Ventilation

It covers requirements and methods for lighting and ventilation of buildings.

Section 2: Electrical and Allied Installations

It covers the essential requirements for electrical installations in buildings to ensure efficient use of electricity including safety from fire and shock. This section also includes general requirements relating to lightning protection of buildings.

Section 3: Air conditioning, heating and Mechanical Ventilation

This section covers the design, construction and installation of air conditioning and heating systems and equipment installed in buildings for the purpose of providing and maintaining conditions of air temperature, humidity, purity and distribution suitable for the use and occupancy of the space.

Section 4: Acoustics, Sound Insulation and Noise Control

It covers requirements and guidelines regarding planning against noise, acceptable noise levels and the requirements for sound insulation in buildings with different occupancies.

Section 5: Installation of Lifts and Escalators

It covers the essential requirements for the installation, operation, maintenance and also inspection of lifts (passenger lifts, goods lifts, hospital lifts, service lifts and dumb-waiter lifts) and escalators so as to ensure safe and satisfactory performance.

Part – 9: Plumbing Services

This part through its two sections gives detailed guidance to concerned professionals/ plumbing engineers with regard to plumbing and other related requirements in buildings.

Section 1: Water Supply, Drainage and Sanitation (including Solid Waste Management)

It covers the basic requirements of water supply for residential, business and other types of buildings, including traffic terminal stations. This section also deals with general requirements of plumbing connected to public water supply and design of water supply systems. Provisions on Rain Water Harvesting have also been included

Section 2: Gas Supply

It covers the requirements regarding the safety of persons and property for all piping uses and for all types of gases used for fuel or lighting purposes in buildings.

Part – 10: Landscaping, Signs and Outdoor Display Structures

Section 1: Landscape Planning and Design

It covers requirements of landscape planning and design with the view to promoting quality of outdoor built environment and protection of land and its resources.

Section 2: Signs and Outdoor Display Structures

It covers the requirements with regard to public safety, structural safety and fire safety of all signs (advertisements) and outdoor display structures including the overall aesthetical aspects of imposition of signs and outdoor display structures in the outdoor built environment. Few more terminologies related to signage and explanatory figures have been added.

Energy Conservation Building Code (ECBC)

The Energy Conservation Building Code (ECBC), launched on 28 June 2007, is a document that specifies the energy performance requirements for all commercial buildings that are to be constructed in India. The code is mandatory for commercial buildings or building complexes that have a connected load of 500 kW or greater or a contract demand of 600 KVA or greater. The code is also applicable to all buildings with a conditioned floor area of 1,000 m2 (10,000 ft2) or greater.The ECBC has been developed by India’s Bureau of Energy Efficiency, and is mandated by the Energy Conservation Act, 2001, passed by the Indian Parliament in September 2001.

ECBC is a set minimum energy efficiency standards for design and construction. ECBC encourage energy efficient design or retrofit of buildings so that it does not constrain the building function, comfort, health, or the productivity of the occupants and also have appropriate regard for economic considerations (life cycle costs i.e. construction + energy costs are minimized).

BEE would take suitable steps to prescribe guidelines for energy conservation building codes. Central Government can prescribe energy conservation building codes, and direct owners/occupiers to comply with them. State Government can modify the code in response to local climate conditions. ECBC provides a platform for the Broad stakeholders such as Building Industry, manufactures, professionals, Government Agencies etc to participate. ECBC addresses local design conditions and construction practices. It also emphasis on maximizing building envelope benefits – to encourage better designs.

ECBC defines the norms of energy requirement per sq. metre of area and takes into consideration the climatic region of the country, where the building is located. Norms have been developed to cater to 5 different climatic zones in India such as composite, hot and dry, warm and humid, moderate and cold.

The ECBC provides design norms for:

• Building envelope, including thermal performance requirements for walls, roofs, and windows, except for unconditioned storage spaces or warehouses.


• Lighting system (Interior and exterior lighting), including day lighting, and lamps and luminaries performance requirements.


• Mechanical systems and equipment, including ventilating, and air Conditioning.


• HVAC system, including energy performance of chillers and air distribution systems.


• Electrical system and motors.


• Water heating and pumping systems, including requirements for solar hot-water systems.

The code provides three options for compliance:

1. Compliance with the performance requirements for each subsystem and system;


2. Compliance with the performance requirements of each system, but with tradeoffs between subsystems; and


3. Building-level performance compliance.

Simulation exercises indicate that ECBC-compliant buildings use 40 to 60% less energy than similar baseline buildings.

ECBC development Process

1. An extensive data collection was carried out for construction types and materials, glass types, insulation materials, lighting and HVAC equipment


2. Base case simulation models were developed


3. The stringency analysis was done through detailed energy and life cycle cost analysis.


4. A stringency level for each code component was established


5. Code was finalized after consideration of comments on a draft version.

ECBC Scope

1. Mandatory Scope Covers commercial buildings


2. Applies to New Construction only


3. Building components included
   
   
   
   • Lighting (Indoor and Outdoor)
   
   
   • Building Envelope (Walls, Roofs, Windows)
   
   
   • Heating Ventilation and Air Conditioning (HVAC) System
   
   
   • Solar Water Heating and Pumping
   
   
   • Electrical Systems (Power Factor, Transformers)

ECBC Compliance Approaches

1. Component-based (prescriptive)

• Requires little energy expertise


• Provides minimum performance requirements


• No flexibility

2. System-based (trade-off)

• Allows some flexibility through the balance of some high efficiency components with other lower efficiency components

3. Whole building design analysis (performance)

• Allows flexibility in meeting or exceeding energy efficiency requirements (as compared to a baseline building)

Building Envelope Design

Impact of Energy Codes

1. Market Development for EE products

• Building Insulation


• Energy Efficient Windows (Glass and Frames)


• High-Efficiency HVAC Equipment

2. Improved Design Practices

• Lighting and Day-lighting


• Natural Ventilation/Free-Cooling Systems

3. Lower Energy Use and Reduced Electricity Bills

4. Reduced connected load and Improved Power Factor

Smart Glass

In recent years, the market for light-controlSmart Glass has expanded due to the increasing demands for energy efficiency and heat and light control, automated shading, privacy, and design and engineering innovation.

Smart Glass or Switchable Glass is a product of cutting-edge technology that allows users to block either all light or just some by simply turning a knob or pressing a button. This type of light control could potentially save tremendously on heating, cooling and lighting costs.

Smart Glass technology basically means controlling the transmission of light through glass by using electrical power. By applying a variable voltage to the glass, the amount of transmitted light can be controlled. Switching speed and the consistency of a tint change are among the most important attributes to potential users of smart glass technology.

The processing technique of Smart Glass is to combine Smart Film with glass through a certain process to ensure reliable use.

Why it is so called?

When a product is called “smart”, it simply means it is programmed with an auto-intelligence capable of operating a single task. And the same goes for smart glass: instead of relying on glass treatments to block the light, these specially designed, energy-efficient glass panes automatically control the sun's solar penetration.

How does Smart Glass Work?

Switchable glass panes dim and brighten at will. When you want sun to shine through your windows, simply flip a switch to turn off the tint. You want to open a room, another flip and the windows will blur, become opaque, or slowly darken. Though they all perform the same task, there are several types of smart glass available. One of the original forms is photo chromatic technology which doesn't require manual operation. Similar to sunglasses, these panes immediately tint when the sun hits, which is efficient since they don't call for any electricity or hands-on direction.

Smart glass technologies include electrochromic devices, suspended particle devices and liquid crystal devices

1. Suspended Particle Devices

Suspended Particle Devices are constructed with two panes of glass separated by a conductive film with suspended, light absorbing, microscopic particles. These microscopic particles within the Suspended Particle Devices (SPD) absorb light, thus preventing it from passing through the film. When the electrical current is added to the film, the particles align themselves to allow light through the glass. The switchable system consists of a non-toxic film between two panes of glass - the higher the current, the more arranged the particles are, and consequently more light is allowed through the glass or plastic.

When the current is switched off, the particles are scattered, inhibiting light penetration. SPD films, which operate off an AC voltage or battery power, consume a very minute power of 0.05 watts/square feet maximum. Users can instantly and precisely control the transparency of the window by manually adjusting a dial connected to a rheostat or automatically setting the opaqueness by programming a photocell.

Smart glass using SPD technology takes several seconds to change from dark to clear, and tint changes are consistent regardless of panel size.

2. Liquid Crystals

Working similarly to SPD technology, these products are black and white: turn it on, they line up to permit light; turn it off, you're in the dark again. Liquid crystal smart glass changes its properties the most quickly of all—from translucent to transparent in milliseconds—and tint changes occur consistently regardless of panel size. Liquid crystal smart glass does not offer a shading benefit, but the view through the glass is blocked when in its translucent state. As such, this product is primarily used for interior needs (e.g., bathrooms) where privacy is required.

3. Electrochromic Glass

Electrochromic Glasses work in the opposite manner. When a current is supplied, they darken and when electricity is withheld they become clear. Another unique aspect of these is that they aren't so black and white. Instead they are able to create varying levels of light penetration, allowing total management of the sun's power. Sometimes it takes several minutes to change shades and typically electrochromic glass works from the outside to the center, but it also doesn't require a constant stream of electricity. Once the initial tint is achieved, no more power is needed.

The switching speed of electrochromic glass is slowest overall and varies depending upon the size of the panel (larger panels typically take many minutes to switch). The consistency of tint changes also varies, with larger panels sometimes exhibiting tint changes that begin at the glazing’s outer edges and then move inward (known as the “iris effect”).

Applications

Smart glass can be applicable in the following areas:

• Several professions and industries such as the house, the fitment and the automobile.
• In the industry of real estate/decoration, it can be applied in high-stand apartments, villas, town houses, office building and stores.
• Building walls, doors, windows and indoor separation, decorations.
• The big area of the projection wall.
• The controllable options of offices (meeting rooms, supervision rooms)
• The controllable options of public facilities (restaurants, hotels, banks, hospitals, the recreational places)
  

Applications of smart glass include building windows, doors and skylights; automobile, boat and aircraft windows; appliance windows, computer screens and cell phone screens. Its use in home and residential windows can all but eliminate the need for blinds or shades, and it fits in with the "green movement" by helping with interior heating and cooling.

Advantages

• Smart glass does not need cleaning and does not fade in the sun like cloth and plastic.
• It only requires a small amount of energy to sustain (powering several windows at once uses less electricity than a single light bulb) and electrochromic glass hardly needs any electricity at all.
• Can assist the air condition to economize energy and can obstruct ultraviolet radiation.
• Allows enough light even when opaque, tenders bright indoors.

Dynamic glazing technologies

Smart glass represents a category of glazing materials that visibly change their properties in response to a stimulus. In doing so, smart glazing in windows, doors, skylights and partitions offer varying levels of dynamic control of light, glare and heat.

1. Passive smart glass

Passive smart glass operates with no electrical interface and is typically found in small-format applications. Self-dimming eyewear that reacts to the presence of ultraviolet light is an example.

2. Active smart glass

The most exciting development in the architectural arena is active smart glass products, including those using liquid crystal, suspended particle device or electrochromic technology. Active smart glass requires an electrical stimulus to change its light-control properties, and power consumption levels are very low. The operating performance of active smart glass depends on the type being considered.

High-performing smart glass products provide unprecedented levels of advanced light-control while also making instant and dramatic design statements. Sleek and innovative, smart glass is tremendously empowering. Just as significant is its array of functional benefits (tunable shading, privacy, glare reduction and remarkable energy efficiency) that support the sustainable design goals of resource conservation and the well-being of building occupants.

Patterned glass

Patterned glass is a kind of decorative translucent glass with embossed patterns on one or both surfaces. Pattern Glass or Decorative Glass or Rolled Glass is generally used where privacy or obscurity is desired but light transmission is still important. With the special property of decoration, patterned glass can allow light to pass through, at the same time, it can also prevent clear view. Usually it transmits only slightly less light than clear glass.

Patterned glass is not-perfectly-smooth structure with different patterns impressed on it. The depth, size and shape of the patterns largely determine the magnitude and direction of reflection.

Basically patterned glass has a pattern impressed on one side of the glass which prevents someone from seeing though it, for privacy. Pattern glass can also be ordered in various tints as well. A common application of this sort is when used in privacy walls to separate one room from another.

Rolled Pattern glasses are available in a wide variety of patterns, to add the perfect complement to many interior designs. Heavy patterned glasses provide added strength and support, and are a fast-growing product category. According to customers' requirements, patterned glass can be cut, ground, drilled, tempered, laminated, etc.

Production

Patterned glass is made with a rolled glass process. All rolled patterned glass begins as a batch of materials, including silica sand, soda, and lime. These materials are melted together in a tank, and then the molten glass mixture is fed onto a machine slab. The glass flows under a refractory gate which controls glass volume and speed then moves between two counter-rotating, water-cooled rollers. One of these rollers is embossed, imprinting a distinct pattern onto the soft surface of the glass while the other roller is smooth.

The result is a piece of glass that is patterned and textured on one side, while smooth on the reverse. The distance between the two rollers determines the ultimate thickness of the glass. After it moves between the rollers, patterned glass is annealed or cooled slowly in order to remove any residual stresses. Rolled patterned glass can then be cut into standard sizes or cut into customized sizes for a specific customer application. The glass is then inventoried and ready for delivery.

Applications

Rolled glasses are used in commercial, residential, and specialty applications. End uses include shower doors and tub enclosures including frameless shower doors interior partitions, translucent door and window treatments, foyers and vestibules, patio furniture, shelving, decorative furniture, and lighting fixtures. Comprehensive range of soft natural colours compliments and harmonizes with modern building materials to provide an exciting and different look to new and existing buildings. Pattern glasses are available in large amount of patterns. Patterned glass is most often found in bathroom windows.

Patterned glass is applied to all kinds of public and private places, such as office, meeting room, hotel, hospital, bath room, washroom, etc. It is also widely used as glass table, glass shaft and lampshade and so on. Mainly used in interior partitions, interior design, decorations, street furniture etc.

Chemically strengthened glass

Chemically strengthened glass is a type of glass that has increased strength as a result of a post-production chemical process. Chemical strengthening is the name given to glass products that have been strengthened by means of an ion-exchange process. It is a surface treatment which occurs at a temperature lower than glass melting temperature. The process is particularly useful for thin glass, tiny glass and shape glass which cannot be tempered by ordinary physical tempering.

Chemically strengthened glass is typically six to eight times the strength of float glass. In the case of breakage, chemically strengthened glass breaks into bigger pieces which are not as sharp as those of non-toughened glass. The surface compression condition which is higher in the case of a chemically strengthened glass also involves an increase of flexion resistance, which is one of the main characteristics of chemically strengthened glass.

Chemical strengthening results in a strengthening similar to toughened glass. Chemically strengthened glass has little or no bow or warp, optical distortion or strain pattern. This differs from toughened glass, in which slender pieces can be significantly bowed.

Chemically strengthened glass may be cut after strengthening, but loses its added strength within the region of approximately 20 mm of the cut. Similarly, when the surface of chemically strengthened glass is deeply scratched, this area loses its additional strength. Chemically strengthened glass retains its colour and light transmission properties after treatment.

Chemically strengthened glass offers an improved scratching, impact and bending strength, as well as an increased temperature stability.

Manufacturing process

The glass is chemically strengthened by a surface finishing process. The glass to be treated is dipped into a bath of dissolved potassium salts at a temperature about 380oC for duration from 4 to 30 hours, producing an ionic exchange between the superficial sodium ions in the glass and potassium ions inside the bath. The cycle time would be greatly reduced if the glass is made of certain elements such as lithium or magnesium because ion mobility between potassium and these elements is a lot faster. The process parameters such as ion exchanging time and temperature would be modified according to the type of glass to be treated and the required strengthen specification.

The introduction of potassium ions which are larger in size than the sodium ions results in the establishment of a system of residual stress characterized by compression stretches on the surface counterbalanced by traction stretches within the glass

Sodium ions and thus, creates stress on glass surface. During cooling, the potassium on surface shrinks little while the sodium in inner shrinks larger. Hence, stress is induced between glass surface and inside and consequently, the glass is strengthened.

Advanced process

There also exists a more advanced two-stage process for making chemically strengthened glass, in which the glass article is first immersed in a sodium nitrate bath at 450 °C, which enriches the surface with sodium ions. This leaves more sodium ions on the glass for the immersion in potassium nitrate to replace with potassium ions. In this way, the use of a sodium nitrate bath increases the potential for surface compression in the finished article.

Classifications

Chemical strengthened glass is classified by two strength components: surface compression and depth of layer (DOL). Surface compression values relate to flexural (bending) strength (MOR), impact strength, hardness penetration (scratching) and thermal shock resistance. Depth of layer values relate primarily to the amount of sustained abrasion resistance and the impact resistance of the surface compression layer.

Applications

Chemically strengthened glass was used for the aircraft canopy of some fighter aircraft. The chemically treated glass boasts a transparency range from the UV through the visible and into the infrared. This permits weapons systems designers to operate guidance devices whether they are CCD, radio frequency, infrared or laser based. The material's proponents stress that chemically treated glass is not just for use in military applications.

It can be used in numerous applications that demand toughness and optical clarity. The material is also useful for viewports, protective covers, and front surface optics in hostile environments whose elements may include high temperature, high pressure and vacuum conditions. Less demanding applications include point of sale scanner windows used in grocery store and retail scanners.

Wired Glass

Wired glass is a type of glass into which a wire mesh is embedded during production. Wired glass has an impact resistance similar to that of normal glass, but in case of breakage, the mesh retains the pieces of glass. This product is traditionally accepted as a low-cost fire-resistant glass. Wired glass can be tinted by aerosol or electricity. Common colours are golden-yellow, green, light blue and violet-rose.

Wired glass is manufactured primarily as a fire retardant, with wire mesh inlaid in the glass to prevent it from shattering and breaking out under stress or when exposed to high temperatures. With the window intact, the glass keeps the fire at bay, protecting those on the other side from the harmful effects of smoke and flame.

However, in recent times, experts warn against the use of wired glass as a fire-resistant substance. This because although the mesh may prevent the fire from penetrating, by itself it could prove dangerous, being made of fine, sharp wires which can hurt. Today, special fire-resistant glass is available, which is devoid of the wire mesh as a component and can cut off not just the fire but even smoke, gases and deadly radiant heat.

Wired glass is made as a part of the rolled glass manufacturing process. Rolled glass is manufactured by passing molten glass from a furnace through a series of rollers to obtain the desired thickness and pattern. The rolled glass process is used to create wired glass, figured or patterned glass, and art/opalescent/cathedral glass.

Wired glass is produced by continuously feeding wire mesh from a roller into the molten glass ribbon just before it undergoes cooling. A steel wire mesh is sandwiched between two separate ribbons of semi-molten glass, and then passed through a pair of metal rollers which squeeze the "sandwich of glass and wire" together. Wired glass may be further processed by grinding and polishing both surfaces, producing "polished wired glass”.

Dichroic glass

‘Dichroic glass’ is really a misnomer. The dichroic part is actually a very thin film of metal oxides which are too thin to stand alone and have therefore been layered onto a sheet of glass which acts as a substrate to lend the thin film strength. Dichroic glass is any glass that is coated with metallic oxides such as silicon, titanium and magnesium in a vacuum furnace using a technology called thin-film physics. Dichroic means 'two colors' and the glass is called this because it reflects one color but transmits another.

Dichroic glass is a high-tech spin-off of the space industry. "Dichroic" is defined as the property of having more than one colour, especially when viewed from different angles or from transmitted to reflected light. Hence dichroic glass is also referred to as "chameleon glass". For example, a particular formulation will appear blue, but shift the dichroic glass slightly and the color will transition to green.

Dichroic coated glass is produced by a process called "thin film physics" and is generally referred to as a colour separator. It's normally used as an interference filter in scientific measuring or correcting applications. It is transparent, has adequate rigidity, is stable, withstands relatively high temperatures, and is not affected by moisture, solvents or most acids.

Manufacturing Process

Dichroic Glass is made by applying a surface coating of one or more layers of transparent materials designed to create reflections of a specific wavelength in order to modify an optical effect. The coating itself is completely transparent. Dichroic glass can provide very crisp and vibrant colors.

The most commonly used coating materials are titanium oxides, zirconium oxides, silicon oxides and aluminum oxides. They are applied using a method called Vapour Deposition. The deposition occurs in a high vacuum chamber where the glass is suspended in the top of the chamber and rotated. The coating materials are placed in crucibles at the bottom of the chamber and bombarded with an electron beam that is focused and swept over the materials with electromagnetic fields. The heat generated by the bombardment vaporizes the materials, and the vapour condenses on the glass suspended above.

Dichroic coatings create some of the purest and most brilliant colours ever seen in glass. They are fragile and must be protected from abrasion unless they are reheated too close to the softening point. Once heated in this way, the coating becomes very durable. The resulting colour of the glass depends on the sequence of the many layers of coatings. Incredibly, the total thickness of the multi coatings is only between 3 to 5 millionths of an inch. It is a highly technical computerized manufacturing process.

The resulting Dichroic Glass is totally unlike normal coloured glass where light enters and part of the colour spectrum is absorbed, leaving the part not absorbed to be reflected. With Dichoric Glass all light entering is either transmitted or reflected (“dichromatic" means "two-colored"). These two sources have completely different colours, and importantly, the colours alter as the angle of view is changed. This results in fascinating and beautifully vibrant colours.

With the play of light together with its vibrant colour, Dichroic Glass is a prime tool used to add interest to any piece of work or project. With over 45 colours of dichroic doatings available that can be placed on “any” substrate (i.e glass), artists have unlimited freedom of expression.

Architectural Applications

There is an ever growing demand for the use of dichroic glass in architecture. Its resilience to weather and never-fading colors are prime material to enhance office buildings, custom homes, walkways, fountains, skylights, walls, lighting fixtures and more. Dichroic glass is also used in windows and curtain walls. Dichroic glass windows on the external wall maximize the entry of natural daylight.

In Other Industries

Dichroic Glass was originally created for the aerospace industry for satellite mirrors, but it now has many technical uses including lighting, fibre optics, infrared lasers, motion picture equipment, and more.

Acid-Etched Glass

Acid etching is a process that uses a strong acid to cut into another substance. It is used for both industrial and artistic purposes. For example, etching can be used to prepare flooring like cement for painting or refinishing, while artists use it to create detailed pictures on metal or glass.

Acid-etched glass has a distinctive, uniformly smooth and satin-like appearance. Acid-etched glass admits light while providing softening and vision control.

Origin of Acid-etched glass

During the middle ages, acid glass-etching was somehow clouded with controversy since its acid medium, hydrofluoric acid, caused too much of a health risk to the artisans. In fact the acid was so potent that users were found to have been poisoned even by its mere fumes. Accidents most often happened where a skin contact with the acid dissolved into the tissues, which later resulted in mutilation or loss of the artisan’s fingers. As a result, acid etched glass craftsmanship lacked refinement and thus lost its luster as an art collection.

Now, there are etching tools such as swivel knives, pick knives, adhesive masks aside from the squeegee which makes it possible for an ordinary person to work on acid glass-etching.

Acid-Etching Glass production

Acid etched glass is produced by acid etching one side of float glass. Etched glass is created by cutting a design stencil that is made of an abrasive resistant material, such as vinyl or rubber. The resulting stencil is called a resist. The resist is then secured onto the glass to be etched. A blaster gun, powered by an air compressor, is used to bombard the glass with the abrasive. Every part of the glass that is not covered by the resist will take the frosted effect while the parts protected by the resist will remain clear, thus producing a piece of etched glass.

Etching glass - Hydrofluoric acid

Glass is etched by hydrofluoric acid, or by hydrofluoric acid gas. The gaseous acid has the property of producing a surface which resembles ground glass in its appearance; the liquid acid produces clear etching. Etching glass, therefore, consists of 2 distinct branches. First, the production of a dull image on a clear surface (when the gas is used) and second, the production of a clear image on a surface previously ground or dulled by means of the liquid acid.

The glass plate to be etched is cleaned and gently warmed until hot enough to melt wax. The surface is then covered with an equable layer of white wax, by rubbing the wax over it. When cold, the design is cut out of the wax with a graver. A shallow leaden trough, about the size of the plate (but a trifle smaller) is obtained, into which is placed a small quantity of finely - powdered fluorspar. This must be weighed and then gently sifted over the bottom of the trough. To every 2 parts by weight of fluorspar add 3 of good oil of vitriol. Stir quickly with a wooden stick, and place on the hob or other warm place. Vapour will soon rise.

Now the trough is removed and covered over with the waxed and graved plate, wax side downwards. In a very short time, the acid will have etched the bare portions of the glass. When sufficiently etched, remove the wax by melting. To prepare the liquid acid for clear etching, place 2 parts fluorspar and 3 of sulphuric acid in a leaden retort, the tube of which must dip into a leaden bottle half - filled with water.

Apply heat to the retort as long as the water will absorb the fames generated. If a ground glass be prepared with wax, as above, and a ledge of wax or putty be made round it, on pouring the liquid acid on the plate, clear lines on the dull ground will result; or a "flashed" colored glass may, by the same means, a colorless picture on a colored ground can be done. The sheets of clear glass may themselves be dulled by exposing them, without previously waxing, to the fumes of the acid gas.

Applications

Acid etched glass is perfect for both interior and exterior applications. Architecture and construction, like in houses, restaurants, hotels, commercial buildings, etc. They are found in many residential applications such as home decoration like furniture components. Some of the suggested applications are:

• Interior partitions
• Railings
• Shelves
• Shower and bath enclosures
• Doors and windows
• Glass walls
• Kitchens
• Interior and exterior doors

Etched Glass

Decorative glass of the nineteenth and twentieth centuries was sometimes put through a process of ‘etching’ to produce a frosted pattern. Etched glass is the result of intentional and often artistic carving of the surface of glass to leave a white, frosted finish. This technique is used to create designs on the glass.

Etching refers to the technique of creating art on the surface of glass by applying acidic, caustic, or abrasive substances. Etched glass can be found in a wide variety of decorative contexts, including glass doors and windows, furniture, wine bottles, and serving dishes. The skill of the artisan etching the glass will determine the quality and detail of the resulting piece.

There are three ways to create a piece of etched glass:

1. Sand-blasting
2. Acid-etching
3. Chemical etching

Sandblasting

Sandblasting is the act of shooting an abrasive material, such as sand, at a piece of glass. There are three other types of sandblasting techniques: Carving, shading, and surface etching. A combination of all three techniques can also used.

Acid etching

Acid etching uses an acid resistant material to cover areas of the glass that the artist wants protected. Hydrofluoric acid is then applied to the glass to produce the design.

Chemical etching

Chemical etching is another way to produce etched glass and is normally what is found in glass etching kits. Just as in sandblasting, a stencil is used to protect the glass where the etching effect is not desired. Instead of an abrasive, however, a chemical cream is applied to the glass. It is this etching cream that produces the final frosted effect.

Acid etching can create the same appearance as sandblasted glass. One of the major advantages of acid etching over sand blasting is that it can be done simply and without as many tools. A frosting effect can also be achieved using different strengths of acid etching compounds.

Stained Glass

Stained glass could either be a reference to the material of coloured glass or the art of working with it to enhance it aesthetically or functionally. Stained glass has a thousand-year history, throughout which it has been applied almost exclusively to the windows of churches, cathedrals, chapels, and other similar buildings. Traditionally, stained glass is made in flat panels and used as windows. However, the creations of modern stained glass artists include three-dimensional architecture and sculpture.

The term "stained glass" has now been conveniently extended to include domestic decorative objects and even copper foil glasswork. This is exemplified by the famous lamps of Louis Comfort Tiffany.

Chemically, stained glass is glass that has been coloured by adding metallic salts during its manufacture. This is then skillfully crafted into stained glass windows, by arranging small pieces of glass to form patterns or pictures, held together by strips of lead and supported by a solid frame. Various methods are used to enhance the design. The term stained glass is also applied to windows in which the colours have been painted onto the glass surface and then fused onto the glass in a kiln.

Stained glass, as an art and a craft, requires the artistic skill to conceive an appropriate and workable design, and the engineering skill to assemble the piece. A good window must fit snugly into its designated space, must block the entry of natural forces, and, most importantly, must be able to support its own weight! Many large windows of vintage buildings have stood the test of time and remained largely intact for centuries. In this context, the purpose of a stained glass window is not to allow those within a building to see the world outside or even primarily to admit light but rather to control it. For this reason stained glass windows have been described as 'illuminated wall decorations'.