Ferrous sulphate (also referred to as iron sulphate) can be used as follows:
As a colour modifier in natural dyeing
To create interesting rust effects in eco-bundling, eco-printing, contact printing
As a mordant in natural dyeing
Please note: Ferrous sulphate can make fibres rough and can damage fibres so use sparingly and limit contact with fabric to just as long as necessary to achieve the desired results.
Keep left over ferrous sulphate solution in a sealed glass jar for re-use and strain with a coffee filter paper to remove any particles.