Quote Originally Posted by elekm View Post
Uncoated lens are prone to scratches. Coated lenses added a hard layer that protected the glass.

I think that's why uncoated lenses get the reputation for being "soft." Optical glass can't really be soft. Otherwise, it would bend and melt if left in a hot car.

The thing with uncoated lenses is how they were handled over the years. Aggressive cleaning has caused many to have "surface cleaning" marks, which are just minute scratches. I've had several lenses that have been damaged by this.

There also is a natural process called "blooming," which affects some uncoated lenses. The result is that it can help to reduce intralens reflections, although it doesn't protect the lens like anti-reflective coating does.
That's not strictly true, I have many old uncoated lenses and the glass is fine with no scratches. However some of the 1930's lenses used newer glass from Carl Zeiss/Schott that seems to be prone to scratches and atmospheric attack. The lenses I've seen like this are Summars, some Tessars and Novars and it's due to the glass being softer.