Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Prismatic Groovy Concentric Background 5
Source GDJ
A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
Prismatic Triangular Seamless Pattern III With Background
Source GDJ
An alternative colour scheme for the original background.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
U.S.-based National Fire Protection Association standard fire diamond for flagging risks posed by hazardous materials. The red diamond has a number 0-4 depending on flammability. The blue diamond has a number 0-4 depending on health hazard. The yellow has a number 0-4 depending on reactivity. the white square has a special notice, e.g OX for oxidizer.
Source Firkin
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
I’m starting to think I have a concrete wall fetish.
Source Atle Mo
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
This background pattern looks like bamboo to me. Feel free to download it for your website (for your blog perhaps?).
Source V. Hartikainen
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
An alternative colour scheme to the original seamless pattern.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin