One little secret is that there are 'channels' to produce certain tones - this means that for each note (pitch) on a string, you can produce a tone colour by the precise location where the bow contacts the strings. The ranges between the dead centre of the vibrating length of the string to right up next to where the string touches the bridge.

The reason for this is that certain harmonics are suppressed where the bow touches the string - it obviously can't vibrate at that harmonic then!

The classical 'best tone' position is funnily enough, 1/13th - to suppress that particular 'troublesome' overtone - the caesura - but 'folk musos' often have their own 'interesting' ideas on the matter.... :-)

And 'musos (folk/trad/classical) that I classify as "bad"' just allow the bow to waver and wander all over the place (as well as NOT keep the bow at right angles to the strings!) ... as I said - they have some 'interesting' ideas... :-)