Mirror without metal?

[h4tt3n]

Hello folks,

 

Does anyone here know a method to make a mirror entirely without the use of metals?

 

Cheers,

Mike

[Klaynos]

Single wavelength mirrors can be made by layers of dielectric.

[swansont]

Many good mirrors are dielectric (broadband, too, not just single-wavelength)

 

http://en.wikipedia.org/wiki/Dielectric_mirror

 

In fact, in my lab they are preferred. We have used gold and silver mirrors on occasion, but IIRC only because dielectric mirrors were not economically available in the form factor we needed (elliptical mirror for ~45 degree reflection of 2" beam)

 

This has a graph of reflectivity for a few different dielectric coatings from one manufacturer

http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=139

[h4tt3n]

Thanks, both of you. These mirrors do seem to be used for very specialized tasks and require expensive equipment to make. Do you know if it is possible to make a typical bathroom mirror of more every-day materials (except metals)? For instance, I remember a "trick" where you can make any object shine like polished metal by first covering it with soot by holdig it into the flame of a candle and then lower it into a glass of water. Surely it must be possible to make a mirrior using similar techniques.

[Moontanman]

Fish scales ground into a fine powder and applied to a sheet of glass might do the trick...

[John Cuthber]

Why do you want a metal free mirror?

We might be able to think of a different solution.

[StringJunky]

The company 3M make non-metallic foil for that silvery bit on your credit/bank cards,and even all over them but I'll be damned if I can find where you can get it from. You probably need to buy a lot to acquire it. I don't know if that's the dielectric stuff Swansont and Klaynos mention. If you tap on the credit card designs at the top they rotate in sequence:

 

http://solutions.3m.com/wps/portal/3M/en_US/PCB/non-metallic-foil/

 

.

[h4tt3n]

John, I want to make a metal-free mirror because metals are not available to me ;-)

 

Stringjunkie & Moontanman - sorry, that won't work for me, but nice tries!

[StringJunky]

John, I want to make a metal-free mirror because metals are not available to me

 

Can you give us more detail about your restrictions and why?

[Enthalpy]

Dielectric coating equipment is presently inherited from semiconductor technology, making it expensive. I believe it would be cheap if a volume industry demanded it.

 

Look: candy films are presently polyester, metallized on one face. Expensive if made in an apparatus for semiconductor processing, but they developed the same metal evaporation process for complete rolls of polyester foil, like W=1m and D=0.5m and t=50µm, or 4000m². They introduce a new roll, a mandrel, pump to vacuum once, and pass the 4000m² in front of the evaporator in a continuous operation.

 

With some development, a similar machine could deposit multiple layers of dielectric in a single pass on a thin refratory metal film, which can be then glued on the mirror.

 

I doubt it's any cheaper than a metal coating. Covering the whole visible spectrum at varied incidences must be possible, though less common than a narrow band.

[swansont]

You could easily make a crappy mirror out of non-metals. Lots of non-metals reflect, it's just that their reflectivity is from an index change, so the value is small compared to what you get from a metal or dielectric mirror. Glass reflects light. The surface of water reflects light (and you could make a concave mirror if it were rotating; people have done that with mercury). But the requirements that it not use conductive material (which is why metals are reflective) AND be highly reflective AND be cheap over-constrain the problem.

[h4tt3n]

 

Can you give us more detail about your restrictions and why?

 

Well, it's complicated. First of all, I am an old-fashioned blacksmith, and I even smelt my own iron viking age style, in a clay furnace. Metal - and especially iron and steel - is my life. I litteraly think in metal. I supposed this has backfired and made me very interested in how to make everyday tools without using metal. Also, a few years back I read a very fascinating sci-fi short story about a society that had no access to metal and thus had to come up with all sorts of alternatives, like bone, cheramics, glass, and so on. I don't know if it makes any sense or if you think I'm weird. I have just found it a very thought provoking mental practice to not think in metal

[StringJunky]

 

Well, it's complicated. First of all, I am an old-fashioned blacksmith, and I even smelt my own iron viking age style, in a clay furnace. Metal - and especially iron and steel - is my life. I litteraly think in metal. I supposed this has backfired and made me very interested in how to make everyday tools without using metal. Also, a few years back I read a very fascinating sci-fi short story about a society that had no access to metal and thus had to come up with all sorts of alternatives, like bone, cheramics, glass, and so on. I don't know if it makes any sense or if you think I'm weird. I have just found it a very thought provoking mental practice to not think in metal

 

Ah, it's an academic exercise...nowt wrong wi' that!

[swansont]

I should add to my previous comment that for the reflections based on an index difference you do a lot better at grazing incidence than head-on (except near Brewster's angle for light polarized with the component perpendicular to the reflective surface)

[StringJunky]

What property of a material, at the photon-election level, causes the photon to be reflected back rather than pass through like in a transparent material? I know, from Feynman, in a transparent material, the energy of the photon is insufficient to energise the the electron to the next level so it drops back down and the photon is re-emitted in a forwards direction, mostly. How does it work with mirrors since the photons are mostly sent backwards?

Edited December 20, 2012 by StringJunky

[h4tt3n]

I should add to my previous comment that for the reflections based on an index difference you do a lot better at grazing incidence than head-on (except near Brewster's angle for light polarized with the component perpendicular to the reflective surface)

 

@Swansont. Yes I noticed this when repeating the soot-in-water mirror experiment last night. The effect was much better when looking along a line near-parallel to the soot-covered surface than when looking along a perpendicular line. I don't think the soot method will work, but I need to do a few more experiments to be sure.

 

Also, you have a very good point in mentioning that reflective materials are so because of their conductivity, which explains why a non-metallic mirror is difficult to make.

 

Also, wouldn't it be possible to make a perfect mirror with a huge prism? Imagine it is shaped as a right angled isosceles triangle (correct term?) and you look into it through the side opposite to the right angle. I even think this prism would reflect the image correctly, and not "mirror" it. Here's an image:

 

 

 

Cheers,

Mike

[swansont]

Also, wouldn't it be possible to make a perfect mirror with a huge prism? Imagine it is shaped as a right angled isosceles triangle (correct term?) and you look into it through the side opposite to the right angle. I even think this prism would reflect the image correctly, and not "mirror" it. Here's an image:

 

 

 

Cheers,

Mike

 

Yes, there are things called corner cubes, which rely on total internal reflection. There are three reflections in them, and since they are beyond the critical angle, all the light that makes it into the device gets reflected.

 

http://en.wikipedia.org/wiki/Corner_reflector

[StringJunky]

Submarine periscope prisms don't use metallic-mirrored surfaces due to them being vulnerable to saline conditions, relying on internal reflections within the prisms instead. I thought that info might contribute to your "non-metallic-mirror databank".

 

A simple periscope without intermediate lenses:

 

 

http://upload.wikimedia.org/wikipedia/commons/thumb/6/68/Periscope_simple.svg/500px-Periscope_simple.svg.png

Edited December 21, 2012 by StringJunky

[ox1111]

I still don't know what you want it for? People in the old days used a bowl or water to see to comb their hair, depending on the bowl it can be very reflective. Automotive paint is very reflective with no metal depending on color and type.

Soot is carbon, graphite is carbon and is metal. How far are you taking this no metals thing.

[Bill Angel]

You could utilize iridescent soap bubbles, or the bodies of iridescent insects.

[Przemyslaw.Gruchala]

Does anyone here know a method to make a mirror entirely without the use of metals?

 

Take glass and use silver color nail varnish on one side