can someone give me a brief rundown on how wide a variety of chords a violin can play.

Hey one of my next projects is a 3 voiced Fugue for two violins. could someone give me a quick rundown on how effective double stopping is in violin writing. EG how easy or difficult it is to move scales in thirds fourth etc

Great much appreciated.

Anything between unison and octaves are safe. Further up the fingerboard you can probably get a 10th. A good player will manage scales in 3rds, fourths, sixths, etc. Don't forget that no double stops are possible where the upper note is below D4, like C# above middle C is played on the G string. Also if one string is open you can get bigger intervals. 

Edit: Forgot to mention that double stop harmonics are more difficult. Keep them to 4ths 5ths and 6ths, They need 4 fingers on the fingerboard. Have a listen to the 3rd movement of Paganini's Vn Concerto No 1 to find out what can be done but remember, there aren't many Paganinis about!