You handle the controls with care. When you see some iron filings forming erratic localized magnetic fields that interfere with the other iron filings – and with your magnetic nub, you do not shake – but you utilize the controls with precision and authority, as to provide the least amount of disturbance to the other iron filings going about their business, drawing themselves.
What will the final picture look like? The sketching continues as the filings draw themselves into unexpected patterns on occasion and it is ever changing. New patterns emerge continually and the process is ongoing.