A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
From a drawing in 'From Snowdon to the Sea. Striking stories of North and South Wales', Marie Trevelyan, 1895.
Source Firkin
This metal background pattern resembles a metal plate with rivets. Solid rivets on a metal plate.
Source V. Hartikainen
Old China with a modern twist, take two.
Source Adam Charlts
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Derived from a PNG that was uploaded to Pixabay by nutkitten
Source Firkin
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Prismatic Chevrons Pattern 5 With Background
Source GDJ
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
Light gray paper pattern with small traces of fiber and some dust.
Source Atle Mo
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Sort of reminds me of those old house wallpapers.
Source Tish
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
The original enhanced with some gradients.
Source Firkin
A seamless paper background colored in pale yellow.
Source V. Hartikainen
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Prismatic Polyskelion Pattern No Background
Source GDJ
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
Produced using the clouds, flames and glass blocks plug-ins in Paint.net and the resulting .PNG vectorised with Vector Magic.
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen