Our wools and threads are dyed with natural plant dyes, and contain no heavy metals.  Some of the plants are local (eg, fern, coreopsis, cammomile), and others (eg, madder, indigo, cutch, brazilwood) are imported from Griffin Dyeworks  and Textile Arts (hey, who else could we buy from?).  They are nice friendly people, and we highly recommend their products. 

A mordant is a substance which opens up the grain of the fibres to let the dyes penetrate.  Alum (Potassium Aluminium Sulphate) is one of the commonest of mordants.  It's non-toxic, and can actually be used as lawn fertiliser.  The other mordants we use are Copper Sulphate (don't drink this one unless you wish to be immediately ill :-),  tin (Stannous Chloride, don't drink this one either), and iron (Ferrous Sulphate) or rusty water, all used in tiny quantities.  Alum brightens colours, copper brings out green, tin brightens and yellows, and iron darkens.  Tin is not used in our Steiner/Waldorf colour palettes.

The dye materials (flowers, leaves, bark, roots) are chopped up and simmered in water for an hour or two.  The dyebath is then strained, and the pre-mordanted fibre put in and simmered for half an hour to a couple of hours, depending on the dye and colour strength desired, or even left cooling overnight.  The fibre is taken out, cooled, rinsed thoroughly, and dried.  It may also get a rinse in an ammonia or white vinegar bath to bring out certain colours;  for example, brazilwood gives purples with ammonia and reds with vinegar. 

Because of variations in rainfall, temperature, and nutrition, colours  from natural dyes will vary from time to time.  The same clump of fishbone fern can give bright yellow in spring and pale green in autumn, for example.  It's always an adventure taking the fibre out and rinsing it -- you can never be quite sure just what you'll get.  Unfortunately this means we cannot guarantee to match colours exactly, so please try to order enough wool or thread for your entire project at once.