If your car has shiny metal parts, you want them in pristine condition to make your car pop. However, before you start cleaning or polishing any type of shiny “silver metal” trim like bumpers, grilles, strips, wheels, hubcaps,…, it’s essential to first determine which is which so you can use the right products and techniques to make them shine.
If you use the wrong product or technique you can make them dull or ruin the finish, especially if it’s a chrome plated or chrome-look part.
We’ll show you how to tell the difference with two simple tests:
Things you might need:
Method 1: Magnet Test
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 uncoated 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 pulling force is about the same as your benchmark, the metal object you want to clean is chrome plated steel (or “chrome” in short). That’s because under that thin layer of chrome (and nickel) there’s a magnetic steel part that is ferromagnetic.
- If there is only a light magnetic attraction, the metal object is (ferritic or martensitic) stainless steel.
Contrary to popular belief, these kinds of stainless steel are slightly ferromagnetic. They are magnetic because of ferrite in their composition and/or their crystal structure. However, they only have a weak magnetic pull compared to iron or (non-stainless) steel. The difference is unmistakable.
- If there is no magnetic attraction whatsoever, the metal can either be aluminum or (austenitic) stainless steel or plastic with a chrome look.
To know which of these three non-magnetic materials you’re dealing with is more difficult: you have to compare and assess the material’s properties.
Method 2: Compare Properties and Appearance
To know if the non-magnetic material is chrome (-plated steel), aluminum, stainless steel or chrome-look plastic, you have to compare its specific properties and appearances to come to a conclusion:
- Weight: Chrome-look plastic is by far the lightest of the lineup. Aluminum comes in second, weighing only about one third of the weight of stainless steel. In turn, stainless steel weighs slightly more than ordinary steel.
- Hardness: Chrome-look plastic is much softer than the other three materials. Chrome is the toughest of the bunch, it’s twice as hard as stainless steel. In turn, aluminum is much softer than stainless steel.
- Color: Chrome has a warm deep blue-ish luster and arguably has the most beautiful reflection. Aluminum has a slightly darker gray appearance, while stainless steel has a lighter silver color. Plastic chrome-look trim can hardly be differentiated from real chrome with the naked eye.
- Sound: Aluminum sounds dull compared to the high pitch ring stainless steel has when you strike it with a steel object. Chrome is somewhere in between, it sounds a little higher than ordinary steel. Plastic does not resonate and has a dull sound.
- Oxidation: If the metal is oxidized and has a really matte, ash gray color or it is (partially) coated in white powder with possible pitting, it is aluminum for sure.
Rust-colored oxidation with possible pitting, bubbling under the shiny top layer and/or flaking means it’s chrome.
Old weathered stainless steel will lose its mirror-like shine and turn matte gray, yet it will never show white or rust-colored oxidation, bubbling or pitting.
Because chrome-look plastic is coated with a special paint to make it look like chrome, it will weather like any coated material: over time the coating will wear, turn dull and/or flake off, showing the plastic underneath.
Now that you know how to differentiate between chrome, chrome-look plastic, steel and aluminum, the next step is to use the right products, techniques and tools to make them shine again. Take a look at our post “How To Clean Chrome, Stainless Steel and Aluminum” for all the ins and outs.
At the risk of boring you guys to death, should you be interested in a more detailed explanation about the differences between silver colored metals, we’ve made an in-depth breakdown on the subject:
In-Depth Look at 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 color. 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.
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 luster that chrome plated metal has. Compared to chrome, SST has a slightly more gray, 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).
Aluminum
Aluminum is the softest and lightest of the three “silver” 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 gray 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 gray 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 colors, of which the natural aluminum color (actually colorless) 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 the non-anodized counterpart.
Fun fact: “Al” in the periodic table of chemical elements is called “aluminum” (/əˈlumənəm/ ə-LOO-mə-nəm) in the US and Canada, while the rest of the English-speaking world calls it “aluminium” (/ˌæl(j)ʊˈmɪniəm/ AL-(y)uu-MIN-ee-əm).
