This wonderful resource book by Jenny Dean is precisely the guide needed for those starting out with Natural Plant Dyes.  The book describes the principles of safety, tools and equipment required, types of mordants and which are best to use with different fibre types.  The book also describes the magic of creating multiple colour shades from one dye pot just by changing the mordants and dye assists such as copper sulphate and iron (ferrous) sulphate.
 
A really great book!