Properties and Composition
Mirrors are some of the most versatile tools available. In the simplest form, a mirror is any reflective surface smooth enough to reflect an image.
Early mirrors were very expensive, as the skills and cost necessary to make a mirror of metal were extensive. An example of the result of an early mirror making technique is the picture of an Aranmula metal mirror above (from http://cs-netlab-01.lynchburg.edu/courses/MACFAST/Indiaweb/Aranmula.htm). Aranmula mirrors are most famous for their lack of distortion, a normal problem with non-glass mirrors. It is very different to create a mirrors such as this using older methods.
To get an idea of this difficulty, take a meter long piece of standard aluminum foil. Fold this into layers until the resulting material is about the size of a person's hand. Using a rolling pin, flatten the material. This step removes the excess air between layers, which otherwise would cause distortion in the images as the mirror is subjected to when exposed to temperature changes. The air and metal expand at different rates, deforming the surface of the mirror. Flatten the resulting mirror as best as as possible, then place it under something very heavy to reduce the distortion from settling as the aluminum fills microscopic voids left by escaping air. How clear is this image? Is there distortion in color, or proportion, especially around the edges? This is typical of even the best solely metal mirror.
In a normal modern mirror, glass or synthetic glass substitutes are backed by mercury, antimony, silver, tin, aluminum or other less common metals. The glass adds extraneous reflections, but makes the mirror more durable and reduces some distortions. To mimic this effect, shape the aluminum mirror created with the previous instructions around one side of glass. Plate glass from windows will work, but a more interesting mirror can be formed with the lens of an old pair of glasses or other curved pieces of glass. Putting the aluminum on the outside of the glasses creates a concave mirror on the inside with a very definite focal point. A set of lenses with focusing prisms, made for a person with some kinds of optical muscle disorders, works even better (a kind friend let me experiment with his). Not only is the resulting image clearer, it is easy to observe the affects covered in the category “Curved” for concave mirrors. As a person's eye approaches the mirror, it first appears smaller then their eye and upside down, then larger than their eye and upside down, is out of focus for a short distance, and then is larger and upright, but flipped left to right.