Wonky Weaver™ Copper Sulphate is a Dye Assist and is usually used to change the colour of a natural dye either as a pre-mordant or post-dyeing colour adjuster.  It changes dull colours like yellow into green, and pinks will turn purple. 
Copper sulphate is gentler on protein-based fibres than ferrous sulphate.
 
Recommended use is between 2 and 4% Weight of Fibre.
This is supplied in a 25g pack