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I just noticed "mirror" was actually created by applying thin layer of metal on top of glass. In fact, the polished metal is exactly how mirror gets its properties - while glass itself is just for structure.

From Wikipedia

The most common structural material for mirrors is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish.

A plate of transparent plastic may be used instead of glass, for lighter weight or impact resistance. Alternatively, a flexible transparent plastic film may be bonded to the front and/or back surface of the mirror, to prevent injuries in case the mirror is broken

So why then this "structure" necessary? Was that because of the metal layer being too thin to stand by itself?

And if that so, then it is possible to create detachable mirror, right? Where metal layer can be detached from it's glass structure

I mean, post-consumer wise, commercial mirror today isn't that easy to recycle.

And its just because of this manufacturing configuration? Or do i missed something?

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    $\begingroup$ When the metal is deposited on the glass, the reflecting surface is protected from the atmosphere by the glass eliminating oxidation. A big deal when the metal used to be silver. $\endgroup$
    – Eric S
    Dec 4 '20 at 22:11
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    $\begingroup$ A water surface can work well as a mirror, no glass at all. $\endgroup$
    – Solar Mike
    Dec 5 '20 at 5:17
  • $\begingroup$ @EricS thank you for that valuable info, was that only consideration? $\endgroup$
    – gijoe
    Dec 5 '20 at 19:28
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    $\begingroup$ I’m not an expert, but it is pretty easy to manufacture smooth and flat glass so it makes an effective surface for a mirror. $\endgroup$
    – Eric S
    Dec 5 '20 at 21:43
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I just noticed "mirror" was actually created by applying thin layer of metal on top of glass.

The vast majority of modern mirrors are created by applying a thin layer of metal to the back side of the glass or transparent plastic.

With all the mirrors in my house and my car, if I look closely at a speck of dust that recently fell through the air onto the front (outer) surface of the mirror, I appear to see 2 specks of dust, separated by a small gap -- the actual speck "floating" on the transparent plastic or glass, and its reflection.

In fact, the polished metal is exactly how mirror gets its properties - while glass itself is just for structure.

You might think that the metal is polished to a flat, reflective surface, and then later the glass is attached to the metal.

With the vast majority of modern mirrors, they are manufactured in the opposite order -- the glass is polished or otherwise manufactured to give an optically flat surface, and then afterwards liquid metal is poured or painted or sputtered onto what will become the back side of the glass.

...

So why then this "structure" necessary? Was that because of the metal layer being too thin to stand by itself?

Yes, that is one of the several reasons -- silver is expensive, so we try to use as little as possible to cover the entire mirror, and that thin foil of silver cannot stand up by itself.

But also, silver is much easier to scratch than glass, so using a harder material like glass helps prevent the mirror from getting scratched up.

And if that so, then it is possible to create detachable mirror, right? Where metal layer can be detached from it's glass structure

I mean, post-consumer wise, commercial mirror today isn't that easy to recycle.

I've heard that "front surface mirrors", also called "first surface mirrors", exist, but they are rare and difficult to clean without damage. They're used in a few telescopes and a few other precision instruments.

With a front-surface mirror, you would be right. With a front-surface mirror, it doesn't matter what material structure is behind it. And you are right that if we simply made the structure behind it the same kind of metal as the optical reflecting surface, such a homogenous slab of material would be easier to recycle than two very different materials -- metal and glass -- bonded together.

And its just because of this manufacturing configuration?

There are other reasons.

The purpose of a mirror is to faithfully reflect all the light that hits it. For reasons I won't go into here, the higher the conductivity of the reflective material, the more light it reflects (and the less light is absorbed into or transmitted through the material). (One major exception is dielectric mirrors).

The most conductive material we know of (at room temperature), and hence the most reflective material we know of, is silver.

Alas, as you may have seen with real silver silverware, silver soon tarnishes when exposed to the air.

Sputtering (untarnished) silver onto glass or clear plastic lets us see the untarnished surface of the silver, and isolates that surface from the air to prevent it from tarnishing.

Compared to silver-backed glass, all other techniques for manufacturing mirrors are generally reflect less light:

  • Some front-surface mirrors use silver, which quickly tarnishes and becomes far less reflective (and generally optically irregular).
  • Some mirrors use silver behind transparent plastic, which is more easily scratched and scuffed than glass.
  • Some mirrors use some other non-silver metal, which inherently is less reflective than polished silver. (aluminum is used in some instruments that require a front-surface mirror, because they don't tarnish and are far more reflective than tarnished silver). (automobile mirrors often use chrome-backed glass, because chromium costs less and they don't need to be as reflective).
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Before we know about other types of mirrors alternative to glass mirror, let's just know about the specifications of traditional glass mirror. Also, before I continue let me assure that glass is though the best alternative in comparison to others: First, the cost matters and the durability and reflectivity is all what makes a mirror useful.

We know mirrors applications in medical field, industries and household. As we already know a mirror is nothing more than just a thin coat of metal on a piece of glass. Glass itself doesn’t provide you with reflectivity. It is the metal that provides the necessary shine and reflectivity to glass.

Mirrors are manufactured by applying a reflective coating to a suitable substrate .That substrate is almost exclusively just glass (because of durability and perfomance), and the reflective coating is typically silver or aluminium.

Because metals oxidize, they can be additionally coated with some tin chloride or paint. A good mirror will always be protected with a frame to avoid damaging the edge of the glass. Glass is a high quality material so It doesn’t age at all, it doesn’t require a lot of maintenance and it is not very expensive as some of the other mirror alternatives.

However, there are many alternatives to this age old idea of having glass mirrors one can use: Plastic mirror- these mirrors are common in children toy or in showpieces. Actually, mirror can be made without any substrate we just have to polish a sheet of metal to a high degree and it will reflect very well. These kind of mirrors so exists and are used throughout world. But usually serve just a decorative purpose rather than being a sort of a tool. These mirrors though are not as reflective as glass mirror but the main purpose of such mirrors are that they don't shatter to often so it's safe for children's use.

Metal mirrors- These are also an alternative to glass but metal mirror would reduce its polish easily it is almost impossible to not introduce micro scratches that will reduce reflectivity. Also, the most galvanized metal mirror will be made of silver, so the cost will be very very high in comparison to glass.

Acrylic mirrors- The most well-known mirror alternative on the market. This type of mirror is actually preferable to a glass mirror for certain situations. The most interesting feature of this mirror is that it is flexible. This makes these mirrors very hard to break. They won’t shatter as glass will, and they will be capable of withstanding bumps and dings. Though acrylic is not as rigid as Glass, drilling a glass is tougher in comparison to drilling a acrylic mirror, as glass mirror will be in risk to shatter apart. As per durability and performance still glass is the winner because glass won't bend stay straight and reflects better.

In conculsion, glass is the most suitable material to make mirrors since plastics scratch too easily and metal are expensive and heavy, acrylic may bend gives less shine.

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    $\begingroup$ Welcome to engineering.SE. Your answer would benefit from some formatting, as of now this wall of text is difficult to read. $\endgroup$ Feb 24 at 8:50
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    $\begingroup$ Use 2 x <Enter> for paragraph breaks. In English there is no space before punctuation ('.'). $\endgroup$
    – Transistor
    Feb 24 at 11:48

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