Double-stops, three and four-note chords all pose challenges for the bow as well as for the left hand.
From the string
When the speed allows, set the bow on the strings before each chord. This gives great clarity to the sound and technical security to the passage.
Even when you play with the chords coming from the air, it is useful to practise them starting on the string in order to check the coordination and give in the bow hand. You can also practise like this using up-bows instead of down-bows.
When playing chords in a 2 + 2 pattern release the pressure after playing the first notes and reapply when you arrive on the top two strings.
Use only a small amount of bow on the bottom two notes and cross early in the bow so that you have enough bow for the top two strings. Use bow speed rather than pressure on the top two strings.
Landing from the air
In some types of chord playing the bow is not set on the string first but lands direct from the air. These include three-note chords at a fast tempo, and double-stops that require the extra energy that comes from landing from the air. (See Bruchs Violin Concerto, 1st movement).
When landing from the air the give in the bow hand is crucial for producing a ringing sound. A supportive 4th finger and a released 1st finger and thumb are essential.
Speed not pressure
Even though both the string and the bow hair will give there is still high friction at the point of impact. Therefore adding any further pressure to the string will usually make the sound crack. For a resonant sound use enough bow and a fast bow speed with no added pressure.
Voicing of chords
Often one of the two lines in a passage of double stops is more important than the other. To emphasize this line we can favour one of the strings by applying more friction to it or by using a slightly crooked bowstroke to vary the point of contact between the strings.
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