Polished Aluminium Tube Section

Aesthetically, this object is somewhere in between a plumbing pipe and a funhouse mirror. It is a piece of thick aluminium tube, polished to a mirror-like appearance. Tubes like this are used as structural support in buildings, across various industries (automotive, transport, furniture, signage, etc.), and by creative hobbyists. It is made of an aluminium alloy from the 6000 series, meaning that magnesium and silicon have been added to the aluminium to improve the mechanical properties of the material (pure aluminium being too soft to use on its own), particularly its surface hardness. 

Polishing is a difficult and time-consuming process, particularly with aluminium, as it is relatively soft and scores so easily. It typically involves rubbing the metal with sandpaper or scouring pads, first very coarse then with finer grits. At the very end, a paste with abrasive powder in it is used to remove the finest irregularities on a polishing wheel. 

Aluminium is excellent at bouncing back any visible light that hits it; this is why it is commonly used to make mirrors, which are essentially a thin aluminium film on the back of a glass sheet. It is also excellent at reflecting infrared light, a type of light we can’t see but perceive as heat; this is why it is also used to make safety blankets, which are another thin film of aluminium coated onto a flexible plastic sheet. Any aluminium surface will reflect light and heat with very little loss. In addition, if that surface is polished, the losses will be even smaller, and the reflection will happen at a very precise angle, giving the material a mirror finish instead of scattering the light in all directions.

This tube was made through extrusion, the familiar process of pushing material through a hole: we are doing extrusion every time we squeeze toothpaste from a tube. In the industrial version, plastics, foodstuffs or metals like aluminium can be made into very long objects with a fixed profile including square rods, round bars and the I-beams that hold up many of our buildings. This is done by pushing material through a die, the hard metal tool which gives the extruded material the desired profile (just like bronze dies turn pasta dough into fusilli, linguine or penne shapes).