Blades of real swords will develop rust (if not well taken care of) and they’re also magnetic. They’re made of plain carbon steel or alloy steel (carbon steel with small amounts of alloying elements).
The blade above is from the Kamakura period. You can see that it’s almost completely covered in rust.
In the photo below, you’ll see the blade has several rust spots. If you look closely, you’ll also see our fingerprints rusted on it. When we provide the maintenance instructions to our customers, we advice them not to touch the blade (sweat and oil from our skin are acidic). But we know it’s inevitable not to touch the blade. We touch the blade of our sword when we do iaijutsu. That’s why it’s important to immediately clean the blade when you or someone else touched it, you don’t want your fingerprint rusting on the blade.
If a blade doesn’t rust and non-magnetic, it means it’s made of either stainless steel or aluminum. If that’s the case, it’s not considered a real sword.
There are swords with blades made of aluminum, like Japanese made iaito, but they’re just training swords. They’re only used for practicing of forms in iaido or iaijutsu; they cannot be used for cutting.
Stainless steel is good for knives. However, if a stainless steel blade is over 12 inches, it’s considered to be too brittle for serious usage as a sword blade. As such, it’s not a good material to be used for functional swords. There’s nothing wrong if a sword has a stainless steel blade, provided you know exactly what you’re getting – a wall hanger or a sword-like-object that’s purely for display or decoration. The issue is, there are a lot of sellers selling swords with blades made of stainless steel that comes fully sharpened. If a blade is fully sharpened, we assume it’s usable, and that’s where the problem lies. A stainless steel blade may snap or break when you use it for cutting, and the tip will go flying away, hurting yourself, bystanders, or pets that are nearby.
A lot of you may have already seen this infomercial where they were selling a “practice katana”. The host was hitting the table with the blade and then it snapped and tip of the blade hit him! If you haven’t seen this video yet, you can watch it in the link below.
There are some swordsmiths in the US who are able to make a functional sword blade made of stainless steel, but it costs thousands of US dollars. You just won’t find a functional sword with a stainless steel blade that costs only PHP 1,000 or PHP 2,000.
Blade maintenance is part of owning a real sword. With proper maintenance, your sword will last a lifetime.