Table of Contents
Which is Which?
Before you start cleaning or polishing any type of shiny “white metal” trim like bumpers, grilles, strips, wheels… it’s essential to determine which is which so you can use the right products and techniques.
To determine what kind of shiny metal you’re dealing with, let’s first start with the magnet test. Take a strong magnet and assess its magnetic power: stick it against any object that is steel for certain, pull it off and get a feel of how much power that took.
Now you have set a benchmark of what the magnetic pull of your magnet on steel feels like.
With that benchmark, it’s time to test it on the metal you want to clean:
If the magnetic power is about the same as your benchmark, the metal object you want to clean is chrome plated steel (or chrome in short).
If there is only a light magnetic attraction, the metal object is (ferritic) stainless steel.
If there is no magnetic attraction whatsoever, the metal you’re dealing with is aluminum or (austenitic) stainless steel.
Telling these apart is less straightforward. You have to compare their specific properties and appearances to come to a conclusion:
- Aluminum is only about one third of the weight of stainless steel.
- Aluminum is much softer than stainless steel.
- Aluminum has a slightly darker grey appearance, while stainless steel has a lighter silver color.
- Aluminum sounds dull compared to the high pitch ring stainless steel has when you strike it with a steel object.
- If the metal is a really matte, ash grey color or (partially) coated in white powder with possible pitting, it is aluminum for sure.
Let’s take an in-depth look:
Different Kinds of Silver Colored Metal
Chrome or Chromium Plated Steel
“Chrome” parts or trim are actually always “chrome plated”.
This means that chrome parts aren’t solid chrome, but there is just a thin chrome coating from 0.0008 to 0.0050 in. (from 0.020 to 0.127 mm) covering the surface.
The chrome or chromium plating is usually applied over a bright nickel plating.
Nickel plating is a very effective anti-corrosion protective layer, but is softer and more difficult to keep clean than chrome plating.
When left to the elements bright nickel plating will turn yellowish gold very fast.
Chrome covers the nickel plating for decorative reasons and to make the part even more corrosion resistant and easier to clean. Chrome plating is very tough and can be polished to a mirror-like shine. Aesthetically, freshly polished nickel has a more yellowish warm appearance than chrome, which has a more cold blue shine.
Old, worn or badly maintained chrome can become dull with pitted rust spots and even flaking. Chrome plating that is worn reveals the nickel plating underneath which looks more yellow than the chrome does and after a while will turn darker yellow because of oxidation, resembling copper colour. Once the nickel is worn or damaged, the steel underneath will start to rust.
Chrome plated metal is the most magnetic of all shiny metals used in the automobile industry.
For a full chrome detailing guide go to “How To Clean Chrome, Stainless Steel and Aluminum“.
Stainless steel
Stainless steel (SST) is a collective name for iron-based alloys that contain a minimum of approximately 11% chromium as a main ingredient, a composition that prevents the iron from rusting.
There are over 150 main types of SST with different characteristics depending on their intended use.
Stainless steel parts or trim are made of solid stainless steel without plating.
Along with chromium, other materials are added in different percentages like carbon, nitrogen, aluminum, silicon, sulfur, titanium, nickel, copper, selenium, niobium, and molybdenum to alter the SST’s properties to be better suited for the intended use.
SST is half the hardness of chrome and more prone to scratching. It is often brushed-polished to make scratches less visible or for decorative reasons.
SST can be polished to a mirror-like shine but it will never have the deep blue-ish lustre that chrome plated metal has. Compared to chrome, SST has a slightly more grey, dull appearance.
Not sure if the material is chrome plated or polished SST? Do the magnet test: if a magnet sticks hard to the metal object, like it would to steel, it is chrome plated. If the metal is not magnetic or there is just a very weak attraction, it is SST.
Contrary to common belief, certain kinds of SST can have magnetic properties depending on their composition or fabrication, but the magnetic force will be much weaker when compared to classic steel or chrome plated metal.
This misunderstanding comes from the fact that SST type 304, which is most commonly used, is non-magnetic.
It is actually the nickel (Ni) content in the SST that renders it non-magnetic (Austenitic SST).
For a full stainless steel detailing guide go to “How To Clean Chrome, Stainless Steel and Aluminum“.
Aluminum
Aluminum is the softest and lightest of the three “white” metals.
Aluminum is never magnetic and is three times lighter than steel.
Aluminum is almost always alloyed (mixed with other metals), which improves its mechanical properties (makes it tougher), especially when tempered (heat treated). This is why this material is often and correctly referred to as “aluminum alloy”.
The main alloying agents are copper, zinc, magnesium, manganese, and silicon, with the levels of other metals in a few percent by weight.
For example: the common aluminum foils and beverage cans are alloys of 92% to 99% aluminum.
Aluminum quickly forms a protective aluminum oxide layer, matte light grey to white with sometimes pitting. The layer forms a protective barrier which protects the rest of the aluminum from oxidation, making it much more resistant to corrosion than steel.
Aluminum alloys are very corrosion resistant and tough, with their lightness as a huge bonus.
While the aluminum oxide is protecting the aluminum from further oxidation, the dull grey appearance is in most cases aesthetically undesirable.
To prevent this layer from forming and keep a glossy surface, often aluminum is factory anodized. Anodisation is an electrolysis process that creates a hard, wear-resistant layer that properly protects the underlying aluminum. Aluminum can be anodized in an infinite range of colours, of which the natural aluminum colour (actually colourless) is the most popular by far.
Freshly polished aluminum will have a mirror-like shine for only a short while. It will become dull very fast because of surface oxidation, depending on external conditions like pH, humidity and galvanic corrosion.
Anodized aluminum will stay shiny much longer compared to non-anodized.
For a full aluminum detailing guide go to “How To Clean Chrome, Stainless Steel and Aluminum“.
Reflectance, Brightness, Gloss
Did you know that polished aluminum is only slightly less reflective than polished silver and still can reflect 90% of light?
Second place in the brightness ranking of decorative metals that are used in the automotive industry is for polished chrome, third place goes to polished stainless steel.
