Dried Finnish birch bark, 500g
This is enough to dye 200g of wool soft pink, and also another 200g a little paler color, and possible more color with further fermenting.
Color is extracted from the bark in alkaline fermentation.
If the barks are simmered without alkaline fermentation the color they give is beige.
Add warm water to the barks, then add washing soda, ammonia or wood ash lye to raise the pH to 10 and leave to ferment in room temperature (or cooler) for 3-4 weeks during which time the pH drops.
After fermenting raise the temperature to 50-60°C for one to two hours. Strain the bath but save the barks to extract more color from them by further fermentation.
Add yarn to the cool bath, and either keep it room temperature for several days or raise to 60°C for couple of hours. Leave the yarns in the bath overnight or longer.
If the yarn was mordanted with alum before dyeing the color should be soft pink, to unmordanted yarn the color is also pink but paler, but this varies in different water.