Titanium isn't all that hard. It is tougher than gold, silver, and platinum, but not as hard as tungsten carbide. It is 6.5 on the Mohs scale of hardness. It can and does scratch at 6.5 Mohs. However, titanium doesn't scuff like iron or bronze. It will always shine like new because it is so thin and light. If you scratch a mirror, then you know how easy it is to scratch glass. But what you might not know is that even though glass is much harder than titanium, people have been learning how to scratch glass for centuries. The secret is in the type of steel used to make knives. If you use a knife that is made from stainless steel, it will not scratch glass. But if you use a knife made from carbon steel, it will scratch glass just like it scratches metal. Carbon steel is more affordable than stainless steel, so this is why most knives sold in stores are made from this material. But if you want a sharp knife that won't leave any marks on your food, then you should probably buy a dedicated cooking tool. Titanium is very difficult to scratch with anything other than your fingernail, and even then it's not easy. But if you manage it, there is no going back. You have scratched something that is supposed to look perfect all the time.