how after restoration of heavily rusted metal objects, they still have so much metal left

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I’ve seen a number of videos recently of people restoring very rusted objects, like toys and an anceint historical knife, where the rust seems to have eaten most of the metal. However, after restoration, the object seems good as new and don’t seem to have lost any significant amount of mass even though you’d expect there to be nothing left. How is this even possible?

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7 Answers

Anonymous 0 Comments

Mass is definitely being lost, but the way rust flakes off it looks like way more is being lost than actually is. I’ve seen pipes that I’d swear were completely compromised and after the rust is cleaned it turns out on 3% of the thickness is actually lost.

Anonymous 0 Comments

Rust is iron oxide; that is, iron atoms combine with oxygen atoms from the air. Furthermore, the iron oxide molecules can bind with several water molecules to form hydrated iron oxide. Also, rust is usually flaky and porous; a lot of its volume is just empty space–but microscopic empty space. So most of the volume you see didn’t come from the iron or steel object itself; it came from the atmosphere.

Anonymous 0 Comments

One point to note, in many cases, rust can also become an external protective barrier that stops further oxidation and keeps the underlying steel protected. ‘Weathing Steel’ is a type engineered specifically to quickly form a solid, protective rust coating. Useful in external structures and gives quite an attractive red finish.

Anonymous 0 Comments

Lots of those restoration videos are faked/artfully edited. Depends on the video. The real art is when people make something intentionally cruddy/mud caked or rusted looking so they can make a fake restoration video.

Anonymous 0 Comments

There are several types of rust actually, and they don’t al penetrante the metal in the same way. Therefore, some steel types just seem to disintegrate while others remain mostly intact. It all has to do with the alloy and surface treatment or annealing it underwent.

Anonymous 0 Comments

When metal rusts, the rust only forms on the surface. When you see metal so rusty that it appears to have bark like a tree, what you’re seeing are extremely thin layers of rust that have piled up on top of each other with lots of space between them. This type of rust is a bit like pastry. Despite its size, there’s very little actual material there.

When restoring a part like this, the biggest problem is surface pitting. Rust can only form where the surface is exposed to oxygen, so the rust actually forms its own protective barrier to some degree, but oxygen is able to find its way in through cracks. The irregularity of the cracks leads to pitting on the surface.

To repair this, you either grind the surface flat, or you apply filler material. Which one you choose largely depends on the surface finish you’ll use. For example, if you intend to paint the item, you can sand it somewhat smooth, then use filler to smooth over the pits, then paint. If you’re going to polish the surface, you have to grind away material until it is flat.

Anonymous 0 Comments

Rust is very unreactive so the rust coating the metal object actually begins to protect the rest of it, so even something “heavily rusted” is only a few atoms deep into the item (indeed something like aluminium oxide forms a layer that’s usually only one or two atoms thick and is extremely unreactive, protecting aluminium from corrosion). There are lots and lots of layers of atoms in an object of any appreciable mass so they don’t lose very much at all when they get cleaned up.