In general it's best to wash your dark colours separately. But it's worth knowing if clothes (especially new ones) are colourfast before putting them in with a regular wash. That way you'll avoid dyes running into other clothes, leaving them an undesirable – and often indescribable – shade!
So check the care label, and do this easy test for colourfastness.
For soaking or washing
- Dampen a small area of hem or inside seam with water
- Iron a piece of white fabric or kitchen paper on to it
- If the paper soaks up any colour, your garment isn't colourfast, so should be washed separately
For solvents (i.e. eucalyptus oil, methylated spirits, white spirit/turpentine substitute, nail polish remover, etc.):
- Dampen an inconspicuous part of the garment with the solvent
- Blot area with a tissue
- If any colour blots off, the garment is not colourfast with the solvent used
Caution: Do not use an iron to test solvents.