One of my favourite studio staples is cheesecloth. I use it for mop-up (the coloured bits are great to incorporate into mixed media paintings), and it's a wonderful tool for creating backgrounds.
I gather my supplies, including a hard support (in this case a wooden panel), brush, paint, water, cheesecloth and water spray bottle.
I create a wash of luscious colour - quinacridone pink is my choice for this demo (the antraquinone blue is SO yesterday),
and lay the cloth over the heavily water-sprayed support. Wetting the cheesecloth with yet more water,
I start laying in a wash of colour with my brush. I'm not too concerned about keeping the colour even, as it will all travel where it wishes due to the watered cheesecloth. You can, of course, also add two or more colours at a time for visual interest.
Once I've sufficient colour on the cheesecloth (and even some of the environs), I leave it to dry overnight.
The next day I can peel the dry cheesecloth off, leaving a subtly gridded background texture behind.