There are many carbon patterns, but this one is tiny.
Source Designova
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868.
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Inspired by an image that was uploaded to Pixabay by geralt
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
Psychedelic Geometric Background No Black
Source GDJ
A seamless pattern formed from a tile made from ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Remixed from a drawing in 'A Girl in Ten Thousand', Elizabeth Meade, 1896.
Source Firkin