Onion Skins are a nice introduction to natural dyes for novices, children, and those who delight in colour from kitchen waste. Red onions give shades of clear maroon-brown on protein fibres and lighter equivalents on cellulose. To obtain satisfying colours from onions skins use at 20% WOF. Simmer for 1 hour, remove the skins and add your mordanted cloth. For a more thorough extraction simmer for an hour then let stand overnight before dyeing. Onions skins have medium fastness.
Mordanting: use alum mordant at 15% WOF for protein fibres. For cellulose mordant with tannin at 8% WOF and then alum at 15%, or alum acetate at 8%.