Tidying up powder designs is often a time consuming process using brushes. One way of cleaning the edges of lines and the bottoms of furrows in the midst of the powder designs is to use a modified keyboard vacuum.
I use a Miele vacuum sweeper –it has a variable suction - with a keyboard cleaning attachment.
I have modified the finest nozzle by putting the end of a ball point pen in it and filling in the remainder of the rectangle with blutac or a similar material. Turn the suction on the vacuum down to minimum and you can be very accurate about the amount of powder you remove to achieve crisp lines.