We considered Bumbershoot, mostly because I wanted to see Edward Sharp and the Magnetic Zeros, but blackberries are nearly done and I had to make a batch of preserves (I almost spelled it "perverses", which may have been appropriate) for gift giving and my own morning toast.
For this batch, I used Pomona's Universal Pectin, which allows one to use a little less sugar to jell the preserves. Two batches, started both with 4 cups of crushed blackberries from the Ballard Farmers Market. Added to that 2t of calcium and 1/4 cup of lemon. The only difference between batches 1 and 2 is that I used slightly less than two cups of sugar in #1 and slightly more in #2. Haven't tasted batch #2 on toast yet, but these particular berries were not sweet, and I'm thinking that a little more sweetness than what I had on my morning toast with batch #1 would have been a good thing. Each yielded about 3 pints of purple deliciousness.