Here's how to dye your own:
Fill a pot with 1 tablespoon of alum, yarn, and enough water for it to be fully immersed. Simmer for an hour. Rinse with cool water and squeeze out excess.
Make Dye Bath
Fill a large pot about halfway with water. Add 1 package of fresh blueberries (squishing them with your hands as you go), and a tablespoon or two of lemon juice to the water. Bring to a boil. Turn heat down and let simmer for an hour.
Use a strainer to remove blueberry remnants from the dye bath. Place yarn in dye bath and push down with tongs or a chop stick, to make sure that it's fully covered by liquid. Let simmer for an hour. At this point if you're satisfied with the color, you can end the process here. Another option is to turn the stove off and let the yarn soak overnight in the cool bath. Your choice.
Rinse & Dry
Remove yarn from dye bath and rinse with cool water until it runs clear. Wash with mild soap and warm water (making sure to prevent felting by not agitating too much). Roll yarn in a towel to squeeze out water, then let dry on a hanger.
That's all there is too it! Since this is still yarn from that same recycled sweater (and my scale's not working), I can't give you an exact yardage recommendation. My guess though, is that I used about 1oo yds for this batch.
If you try and give it a go yourself, I'd love to see pictures of your results! Feel free to post photo links here. Alright, back to business. Enjoy!