Anti-Fogging Glass

Car windows, eyeglasses, camera lenses, even our bathroom mirrors are all victims of the frustrating effects of fogging. Fogging can pose hazard when it inflicts automobile windscreens; glass fogs up when warm, moist air comes into contact with it and cools to form thousands of tiny water droplets on the glass. The droplets scatter light, reducing the visibility through the glass.

Existing Technology

Fog is caused when steam condenses on a cool surface and then forms minuscule water droplets due to the water's surface tension. Water molecules are more attracted to each other than to air molecules and form a spherical shape to maximise contact between water molecules, which leaves as few as possible exposed to the air.

But water is also attracted to glass, and if this attraction is enhanced, it can overcome the surface tension. Previous anti-fog coatings have capitalised on this using titanium dioxide surfaces which increase the attraction between the water and glass. This overcomes surface tension so the water spreads out in sheets.

However, these coatings first need to be charged by UV light which means they do not work for long in the dark. And they tend to stop working altogether after three months.

Latest Anti-Fogging Glass

Super-hydrophillic

Super-hydrophillic - water loving - coating is composed of nano-particles made of silica, the same material that glass is made from, to create a coating with a rough surface, although it looks smooth to the naked eye. Polymer chains are used to assemble these very tiny particles of Glass onto a surface. A polymer chain is a long chain-like molecule with positive charge and the glass particles with negative charge are taken. So positive to negative attractive force can be used to build these layers up onto the surface. The net result is we create a very porous coating, that is, a coating that has lots of holes in it.

The silica particles form layers of tiny pores, each a thousand times smaller than the width of a human hair. The pores attract the tiny droplets of water that make up the foggy surface. Stacked ten to twenty layers thick, with air pockets in between, these pores create what's called a "wicking" effect, which forms the water droplets into a uniform sheet. When a droplet is dropped on that surface, the water is drawn into these pores instantaneously and wicked away into a uniform sheet. The result is no water droplets on the surface that can scatter light and a nice transparent lens in this case.

This cheaply produced technology added benefit of increasing the clarity of unfogged glass. It reduces the glare and allows more than 99 percent of light to pass through the glass, compared to untreated glass that scatters between four and eight percent of light. Because of the thin film coating that is filled with holes, it means that the coating also acts as an anti-reflection coating. That is, it will allow more light to pass through.

The super-hydrophilic materials with self-cleaning action are currently in use for side view mirrors of vehicles and exterior materials of buildings.

Super-hydrophobic

Super-hydrophobic - water-fearing – coating is made by adding a second, ultra-thin layer of water-repelling molecules. Then the large surface area created by the roughness of the surface has the opposite effect. It increases the repulsion between the water and glass, causing the water to form droplets.

These could be used to form self-cleaning surfaces, where water that lands on the surface is snapped up into droplets that grow larger and larger until they finally roll away, taking the dirt with them. This is the method a lotus leaf naturally uses to clean itself.

Application

• Windshields and windows

• Solar panels

• Lenses for cameras, endoscopes, laparoscopes, and other optical devices

• Eyewear – goggles and glasses

• Dental mirrors

Advantages

• Stable over time

• Inexpensive

• Does not require UV-light activation

• Excellent optical properties (high transmittance; low reflectance and refractive index)

Frosted glass

Frosted glass is a glass which has been rendered opaque through a process which roughens or obscures the clear surface of the glass. Frosted glass can enhance the beauty of windows, glass doors, or glass cabinets. This technique adds warmth and style to any décor.

Frosted glass or opaque glass is produced by the sandblasting or acid etching of clear sheet glass. It has the effect of rendering the glass translucent by scattering of light during transmission, thus blurring visibility while still transmitting light.

The frosted glass effect can also be achieved by the application of vinyl film, used as a sort of stencil on the glass surface. "Photo-resist” or photo-resistant film is also available, which can be produced to mask off the area surrounding a decorative design, or logo on the glass surface. A similar effect may also be accomplished with the use of canned frosted glass sprays.

Glass frosting can be accomplished on glass of any colour, and can look quite striking and distinctive. Care should be taken while working with acid to produce frosted glass. Eye and face protection should be worn when making frosted glass.

Various Frostings

A frosted appearance may be given to glass by covering it with a mixture of magnesium sulphate. When this solution dries, the magnesium sulphate crystallizes into fine needles. Another formula directs a strong solution of sodium or magnesium sulphate, applied warm, and afterwards coated with a thin solution of acacia.

A more permanent "frost" may be put on the glass by painting with white lead and oil, either smooth or in stipple effect. The use of lead acetate with oil gives a more pleasing effect, perhaps, than the plain white lead. If still greater permanency is desired, the glass may be ground by rubbing with some gritty substance.

For a temporary frosting, dip a piece of flat marble into glass cutter's sharp sand, moistened with water; rub over the glass, dipping frequently in sand and water.

If the frosting is required very fine, finish off with emery and water. Mix together a strong, hot solution of Epsom salt and a clear solution of gum arabic; apply warm. Or use a strong solution of sodium sulphate, warm, and when cool, wash with gum water. Or daub the glass with a lump of glazier's putty, carefully and uniformly, until the surface is equally covered. This is an excellent imitation of ground glass, and is not disturbed by rain or damp. The production of imitation frosting entails little expense and is of special advantage when a temporary use of the glass is desired.

Manufacturing Process

The frosted glass production requires a thorough cleaning of the glass surface before beginning the frosted glass process.

Frosted glass frosting formula is mixed with wallpaper paste, white powder paint pigment, water, and acid free PVA glue. All ingredients are mixed well, except the glue until having a pudding texture for the frosted glass project. Once this texture is achieved, a drop of glue is added so that the mixture will adhere to the glass.

The stencil should be placed on the glass, using painter's tape to secure it to the glass surface. The frosted glass mixture is applied using a stiff brush over the stencil. This is continued until all of the areas of the glass that we want to turn into frosted glass have been coated.

Applications

• To obtain visual privacy while admitting light.
• Decorative patterns may be imposed upon otherwise plain glass by using wax or other resist to retain transparent areas.
  

A sheet of frosted glass is an excellent privacy aid because it admits light without allowing people to see through it. In medical offices and bathrooms, the use of a curtain or blinds would make a room gloomy and unpleasant to be in. Frosted glass, on the other hand, keeps a room bright and friendly while still allowing people to be comfortable. People may also use frosted glass for privacy in entryways in urban areas.

Commercially produced frosted glass is usually frosted with acid etching or sandblasting. Acid etching is used to make frosted glass with a pattern. Patterned glass sometimes appears in ornamental windows, as well as in glasses, mirrors, vases, and other glassware around the house. The pattern can be simple or extensive, and it may include floral or geometric elements. Sandblasting is used to frost an entire sheet of glass, for installation in places like bathrooms and other areas where people might want privacy.

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.