printing; indentification; letterpress

Printing technology that leaves this grayed, crisp effect?

I have been reading a nice old edition of The Sun Also Rises, by Hemingway. The printing has a peculiar effect, to my eye, which I'm trying to understand.

Namely, this: the type appears somewhat grayish,like a 60% or 70% gray, consistently throughout the book. Looking at the title page and the chapter heads, where the strokes are a bit wider, I can see it is slightly uneven, and also that the very edges of the letters are slightly crisper and darker. It gives a feeling of letterpress, although I'm sure it wasn't printed that way. Certainly there is no impression as would be left by a heavy press. And anyway, it is a mass-produced edition. The text is very pleasant because of this color.