Gather materials that are in your locality. Try to use bio-waste and left over kitchen ingredients, or items that are foraged sustainably. Some of my favourite natural dye ingredients are; onion skins, red cabbage offcuts, turmeric peelings, carrot tops, buddleia, nettles, coffee grinds, and avocado pips.
Soak dried or tough materials overnight. Grind roots and berries. Chop plants into small pieces.
Simmer the prepared materials gently in a stainless steel container with a small amount of water for about half an hour. Leave dye material to cool down. Squeeze through a plastic sieve and/or using a clean tea towel or muslin.Collect the dye liquor. The used plant material can be put onto a compost heap.
The dye liquor can be thickened with common household starch. I like to use cornflour; 8g flour to 100ml dye liquor.