The use of iron filings
1 The filings should not be 'dust' but should have one dimension longer than the other two.
2 The 'pepper pot' shaker must have holes large enough to allow the filings of this size to pass through. It can be improvised from a film can from holes through the plastic lid.
3 Iron filings can ruin sinks. It is wise to cover all sinks in the lab before issuing iron filings.