From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
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
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A seamless background texture of old cardboard.
Source V. Hartikainen
Remixed from a PNG that was uploaded to Pixabay by k_jprather
Source Firkin
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A dark gray, sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Seamless SVG vector and JPG backgrounds with faded diagonal stripes. The colors are editable.
Source V. Hartikainen
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
CC0 and seamless wellington boot pattern.
Source SliverKnight
Bumps, highlight and shadows – all good things.
Source Badhon Ebrahim
Geometric triangles seem to be quite hot these days.
Source Pixeden
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin