Start a Mirror Making Business

Start a Mirror Making Business

  
Whether you are trying out a new dress or wondering if you are really going bald, the first thing you turn to look at is a mirror. From your car to your powder room, from telescopes to televisions, mirrors serve many important functions. This article highlights the types of mirrors, their uses and their structure.

Identification

• A mirror is made by applying a reflective coating to a suitable base surface. Glass is considered the best substrate because of its rigidity, ease of fabrication and smooth finish. The reflective coating, usually aluminum, silver or gold, is applied to the back of the glass surface. The metal chosen for the coating determines the reflectivity of the mirror. Aluminum is the most inexpensive and the most commonly used coating. Silver and gold are more expensive and offer better reflectivity for visible and infrared wavelengths.

Function

• Mirrors are extremely versatile in their function. They're used for cosmetic purposes in dressing rooms and bath rooms. They also provide rear view in automobiles. Mirrors are used for signaling in the military and during rescue operations. Microscopic mirrors are used in HD TVs. Telescopes and other optical instruments too use mirrors. Mirrors play an important role in interior decor. They are used to gather and reflect solar energy in systems that are powered by the sun. Different kinds of "fun mirrors" are used to amuse and entertain people.

  Types

  • The most common type of mirror reflects most of the light that falls on it. Two-way mirrors or one-way glass let part of the light pass through and reflect part of the light. These are what one sees in stores where one reflective side is dark and the other reflective side is bright. Based on the shape, mirrors are classified as concave (like the inside of a bowl), convex (like a bowl turned upside down) and plane, or flat.

  Mirror raw materials - What are mirrors composed off?

  Glass, the major mirror component, is a poor reflector. It reflects only about 4 percent of the light but possess the property of uniformity, particularly when polished. Glass is also considered a good material for mirrors due to its transparency, ease of fabrication, rigidity, hardness, ability to take a smooth finish, and can be molded into various shapes for specialty mirrors. Silica, which can be mined or refined from sand, is used to make glass.

  For the production of high-quality scientific grade mirrors a few other types of glass are used. These types of glass usually contain some other chemical components to make the glass stronger or make it resistant to certain extreme environmental conditions. Pyrex, for example, is a glass composed of silica and boron that is used when mirrors must persist high temperatures.

  To manufacture mirror glass needs to be coated. The most commonly used materials that are appropriate for this application are metal coatings such as silver, gold, and chrome. One hundred years ago silver was the most popular metal coating for, leading to the invention of the term ''silvering''. Before 1940, mercury was the most commonly used metallic coating for mirrors because mercury is spread evenly over the surface of the glass and did not tarnish. This practice was eventually abandoned, because mercury seals in the toxic liquid. Today, mirror manufacturers use aluminum instead of mercury.

  Scientific grade mirrors sometimes use coatings of other materials, like silicon oxides and silicon nitrides, in up to hundreds of layers of, each a 10.000th of an inch thick. These types of coating are used as reflectors, and as protective finishes on metallic coatings. In comparison with metal, they are more scratch resistant. Scientific mirrors are also coated with silver and sometimes with gold, to reflect light of a particular color of light more or less well.

  How Mirrors are Made?

    

  Ancient times, people used obsidian stones to make mirrors. These stones when highly polished were able to reflect with a great clarity. Through times, as civilization evolved, technology did too. Gradually, people started to use gold, silver, and aluminum to create mirrors in the similar manner they used the obsidian stone. In about 1600 AD, the silvering process, which became the most popular way to make mirrors, was introduced and it is used even today.

  In classical antiquity, solid metal (bronze, later silver) was used to manufacture mirrors and mirrors were too expensive; they were also prone to corrosion.

  Venetian glassmakers introduced the process of making mirrors out of plate in 16th century. They covered the back of the glass with mercury to obtain near-perfect and undistorted reflection.

  Today, the mirror substrate is first shaped, then polished and cleaned, and finally covered.

  The method of making mirrors is very simple. Mirrors are made by applying a reflective coating to a glass sheets. Glass is a major mirror component due to its transparency, ease to fabrication, rigidity, hardness, and ability to take a smooth finish but it is not very good material for reflection. Materials which are commonly used are metal coatings such as silver, gold or chrome. Present-day glass mirrors are most often coated with non-toxic silver or aluminum.

  It is very important that the glass is polished to perfection, any dip or impurity left on glass would made waves in the mirror, which would cause distortion of the image reflected.

  There are many methods of glass to be coated with the chosen metal to form a mirror. In industrial productions, glass is coated by bringing the metal to a boil in special chambers and then metal is condensed on the glass sheet to form a thin but perfect coating of the metal. The back surface of the mirror is painted to prevent damage to the metal coating.

  Mirrors have to be specially designed in order to become effective, and the glass sheets that are used must be flat and durable. For household use, the thickness of the mirror is very important, with its strength increasing proportionately to its thickness. For heavy-duty mirrors and mirrors used in scientific research, the surface needs to be designed in particular way to retain uniformity while adding a curvature. This process gives the mirror the ability to focus as well as reflect light. The kind of coating to be used is specified by the mirror design. Durability and reflectivity are the most important characteristics in the choice of the coating.

  An important part of the manufacturing process is the quality control of mirrors. Inspection of the mirror's surface is generally performed using the naked eye or a microscope in order to check if there are any scratches or unevenness.

  Design

  Surface regularity is probably the most important design characteristic of mirrors. Mirrors for household use must meet roughly the same specifications as window panes and picture frame glass. The glass sheets used must be reasonably flat and durable. The designer need only specify the thickness required; for example, thicker mirrors are more durable, but they are also heavier. Scientific mirrors usually have specially designed surfaces. These surfaces must be uniformly smooth within several lOOOths of an inch, and can be designed with a specific curvature, just like eyeglass lenses. The design principle for these mirrors is the same as that of eyewear: a mirror may be intended to focus light as well as reflect it.

  The mirror design will also specify the type of coating to be used. Coating material is chosen based on required durability and reflectivity and, depending on the intended purpose of the mirror, it may be applied on the front or back surface of the mirror. Any subsequent layers of protective coatings must also be specified at this stage. For most common mirrors, the reflective coating will be applied on the back surface of the glass because it is less likely to be harmed there. The back side is then frequently mounted in a

  
  

  The initial step in mirror manufacture involves cutting and shaping the glass blanks. Cutting is usually done with a saw with diamond dust embedded in the tips. Next, the blanks are put in optical grinding machines, which use abrasive liquid plus a grinding plate to produce a very even, smooth finish on the blanks. The reflective material is then applied in an evaporator, which heats the metal coating until it evaporates onto the surface of the blanks.

  plastic or metal frame so as to entirely seal the coating from the air and sharp objects.
  

  For scientific use, the color, or wavelength of light, which the mirror will reflect must be considered. For standard visible light or ultraviolet light mirrors, aluminum coatings are common. If the mirror is to be used with infrared light, a silver or gold coating is best. Dielectric coatings are also good in the infrared range. Ultimately, however, the choice of coating will depend on durability as well as wavelength range, and some reflectivity may be sacrificed for resilience. A dielectric coating, for example, is much more scratch resistant than a metallic coating and, despite the additional cost, these coatings are often added on top of metal to protect it. Coatings on scientific grade mirrors are usually applied on the front surface of the glass, because light which travels through glass will always distort to a small degree. This is undesirable in most scientific applications.

  
  
  

  The Manufacturing Process

  Cutting and shaping the glass

  • 1 The first step in manufacturing any mirror is cutting the outline of the glass "blank" to suit the application. If the mirror is for an automobile, for example, the glass will be cut out to fit in the mirror mount on the car. Although some mirror manufacturers cut their own glass, others receive glass that has already been cut into blanks. Regardless of who cuts the glass, very hard, finely pointed blades are used to do the cutting. Diamond scribes or saws—sharp metal points or saws with diamond dust embedded in them—are often used because the diamond will wear down the glass before the glass wears down the diamond. The cutting method used depends entirely on the final shape the mirror will take. In one method, the blades or scribes may be used to cut partway through the glass; pressure can then be used to break the glass along the score line. In another method, a machine uses a diamond saw to cut all the way through the glass by drawing the blade back and forth or up and down multiple times, like an automated bandsaw. Cutting is usually done before the metal coating is applied, because the coating may flake off the glass as a result of the cut. An alternative to cutting the glass to form blanks is to mold the glass in its molten state.
  • 2 Blanks are then placed in optical grinding machines. These machines consist of large base plates full of depressions that hold the blanks. The blank-filled base is placed against another metal plate with the desired surface shape: flat, convex, or concave. A grinding compound—a gritty liquid—is spread over the glass blanks as they are rubbed or rolled against the curved surface. The action is similar to grinding spices with a mortar and pestle. The grit in the compound gradually wears away the glass surface until it assumes the same shape as the grinding plate. Finer and finer grits are used until the surface is very smooth and even.Hand grinding techniques exist as well, but they are extremely time-consuming and difficult to control. They are only used in cases where mechanical grinding would be impossible, as is the case with very large or unusually shaped surfaces. A commercial optical grinder can accommodate 50 to 200 blanks, which are all polished simultaneously. This is much more efficient than hand grinding. Even specialty optics can be made mechanically in adjustable equipment.

  Applying the reflective material

  • 3 When the glass surfaces are shaped appropriately and polished to a smooth finish, they are coated with whatever reflective material the designer has chosen. Regardless of the coating material, it is applied in an apparatus called an evaporator. The evaporator is a large vacuum chamber with an upper plate for supporting the blank mirrors, and a lower crucible for melting the coating metal. It is so called because metal is heated in the crucible to the point that it evaporates into the vacuum, depositing a coating on the surface of the glass much like hot breath will steam a cold window. Blanks are centered over holes in the upper plate that allow the metal vapor to reach the surface of the glass. Metals can be heated to several hundreds or thousands of degrees (depending on the boiling point of the metal), before they vaporize. The temperature and timing for this procedure are controlled very precisely to achieve exactly the right thickness of metal. This method of coating creates very uniform and highly reflective surfaces.
  • 4 The shape of the holes in the upper plate will be transferred to the glass in metal, like paint through a stencil. This effect is often used to intentionally pattern the mirror. Metal stencils, or masks, can be applied to the surface of the glass to create one or more patterns.
  • 5 Dielectric coatings—either as reflective layers or as protective layers over metal ones—are applied in much the same way, except that gases are used instead of metal chunks. Silicon oxides and silicon nitrides are typically used as dielectric coatings. When these gases combine in extreme heat, they react to form a solid substance. This reaction product forms a coating just like metal does.
  • 6 Several evaporation steps may be combined to make a multiple-layer coating. Clear dielectric materials may be evaporated on top of metal or other dielectrics to change the reflective or mechanical properties of a surface. Mirrors with silvering on the back of the glass, for instance, often have an opaque dielectric layer applied to improve the reflectivity and keep the metal from scratching. One-way mirrors are the exception to this procedure, in which case great care must be taken not to damage the thin metal coating.
  • 7 Finally, when the proper coatings have been applied, the finished mirror is mounted in a base or packed carefully in a shock resistant package for shipping.

  Making a Mirror-O-Matic Mirror Making Machine