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

Question

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?

In: 3

Answer 1

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.