I have knitted several of these. The one pictured is my personal Ravenclaw, in blue and bronze. The films use blue and silver for Ravenclaw, but every True Ravenclaw knows the colors are really blue and bronze. The finished scarf is about 10′ long.
One day, I'll take better pictures of it, under proper lighting. Done with the move to Ghost, 8 June 2014.
The pattern is adapted, with significant alterations, from a pattern that appeared at a site called atypically.knit, which, alas, no longer exists.
CO 114 sts in MC on 16″ US4 circular needles. Use whatever CO method you prefer, I use a cable cast-on. Your CO edge will be covered by tassels when you're done, so it doesn’t really matter.
Set your row marker.
Using 16"; US #4 circular needles CO 114 sts in MC *[Knit in the round for 36 rows in MC. Switch to CC, knit 4 rows. Switch back to MC, knit 6 rows. Switch to CC, knit 4 rows.] Repeat from * 13 more times for a total of 14 pairs of CC bands. Knit 36 rows in MC. Bind off.
I have 14 tassels on each end (I chose that number for symmetry—it’s impossible to tell how many tassels are on the on-screen scarves). Just cut ten or so equal lengths of yarn per tassel, pull them all through at roughly equal intervals and loop ’em. I recommend blocking. Gives a nice smooth finish.
I use Brown Sheep Nature Spun sport weight 100% wool yarn. Here are colors:
Ravenclaw: --MC: N04 Blue Knight (Blue) --CC: N94 Bev's Bear (Bronze) --CC(alt): 107 Silver Sage (Silver) Slytherin: --MC: N25 Enchanted Forest (Green) --CC: 107 Silver Sage (Silver) Gryffindor: --MC: 200 Bordeaux (Red) --CC: 308 Sunburst Gold (Gold) Hufflepuff: --MC: 305 Impasse Yellow (Yellow) --CC: 601 Pepper (Black)
If you want to be hyperpedantic, stills from the Blu-Ray disc show that the scarves in the film are actually
[36-4-6-4]*14-36, but I think the latter looks better.
Edit: I neglected to mention yarn quantities—You will need a cone of MC and four balls of CC. A cone equals ten balls. My source for cones has dried up, but your local yarn shop may be able to order it.