2 Methods of Identifying Metals
Appearance
There are several ways to identify metals, but the most common is the appearance. First check the colour, as well as its visual elements. Brass is yellow and smooth. Copper is reddish in colour and turns green when oxidized, like an old penny. Aluminum is silvery but not shiny, and when broken, it appears coarse grained. Cast iron can be either white or greyish. A broken section will appear very coarse, like grains of sand.
Weight
The weight of metals will also help in their identification. Aluminum is very light. Steel, stainless steel, cast iron, and zinc are heavier. Lead is very heavy.
Ferrous vs. Non-Ferrous
You may determine whether a metal is ferrous or non-ferrous by testing it with a magnet or spark test. Ferrous metals are attracted to a magnet, while non-ferrous metals are not. Stainless steel is the exception, it may or may not be attracted to a magnet, depending on its composition. And all ferrous metals will spark.
Hardness
You can also test the hardness of iron and steel with a file as follows:
| Type of steel | Resistance to filing |
|---|---|
| Low carbon mild steel | Low resistance, file bites easily into metal. |
| Medium carbon steel | Low resistance, file bites into metal, but more pressure needed. |
| High carbon steel | High resistance to file, can only be filed with great difficulty. |
| Tool steel | Very high resistance, can be filed but the metal is almost as hard as the file. |
| Hardened tool steel | Maximum resistance, cannot be filed, metal is harder than the file. |
Characteristics of Metals
Oxides
Some characteristics of metal are determined by their oxides. Oxides can change the appearance and effect the metal’s lasting characteristics, either protecting or destroying it. To “oxidize” is to combine an element with oxygen or convert an element into an oxide. For example, when carbon burns, it combines with oxygen to form either carbon dioxide or carbon monoxide. Oxides are formed on any metal when exposed to the oxygen in the air. For example, iron combines with the oxygen in the air to form an iron oxide commonly known as rust.
Here are some common metals and their oxides:
- Aluminum — Aluminum oxide: A very tough, clear oxide that forms almost instantly, making soldering and welding difficult.
- Copper — Patina (copper sulfate): A very tough, green oxide. May also form in other colours.
- Iron (steel) — Iron oxide (rust): An oxide that flakes off, exposing metal underneath, which will also rust and flake off.
- Lead — Lead oxide: A very tough gray/black oxide that must be removed by scraping in order to solder.
- Stainless Steel — Chromium oxide: A clear, tough oxide that quickly forms and protects the metal.
Electrolysis/Galvanic Reaction
Another characteristic of metals is what’s called electrolysis or galvanic reaction. All metals will go through this process if dissimilar metals are in contact with one another with moisture is present. (Note that moisture is pretty much always present, even in the desert.)
Dissimilar metals must be kept from contacting with one another. Moisture promotes this condition and slowly disintegrates the metals at their points of contact. The severity of corrosion depends on the metals. If we refer to a galvanic chart, the further away the metals are, the worse the corrosion will be.
Media Attributions
- “Statue of Liberty” by Dominique James is licensed under a CC BY 2.0 licence.
- “Spark Test Mild Steel” by Corvi is licensed under a CC BY-SA 3.0 licence.
- “Galvanic Series Chart” by BCcampus is licensed under a CC BY 4.0 licence. Based on a chart by Harrison McCampbell in “Separating Galvanic Materials” in the Journal of Light Construction.
A chemical compound formed by metal and oxygen. Oxides can forms on metals when they're exposed to oxygen.
Metals or alloys that contain 5% or more of iron. Steel and stainless steel are considered ferrous metals.
Metals or alloys that contain less than 5% iron and in most cases, contain no iron (i.e., aluminum, copper, zinc, and lead). Examples of non-ferrous alloys are bronze and brass.
The degree to which a metal can endure mechanical indentation or abrasion without deformation.