Use Ferrous Powder on paintings and mixed media. For a water resistant dark grey magnetic coating, mix up to equal parts of Ferrous Powder to a slurry with MM14 Gloss (turps-based), MM15 Matt (turps-based) or MM29 Satin(turps-based), then seal with the varnish. Ferrous powder can be rusted. Otherwise, mix with MM14 Gloss (turps based) or MM29 Satin (turps based) and varnish to seal. Avoid sprinkling. Large amounts may cause the canvas to sag.