Just a quick follow-up to my earlier report about trials with flax seed-based juice. I have tried a few variants including a double-strength mix (2 tablespoons of flax seed per liter at final dilution). My impression is that the mixes are pretty good but with decent humidty (which is mostly what we have had) that the mixes are inferior to guar gum and PEO and similar mixes. The flax seed goo seems to thicken bubble walls quite a bit (which means more soap to get the soap film into my preferred color zone). The bubbles seem a bit more "brittle" than bubbles made with my preferred polymers in a way similar to what happens when gelatin or xanthan gum are in the mix.
On a few occasions (with fairly low humidity), the flax seed juice seemed to create longer-lived bubbles than a guar-based mix when using a 20" kids' top-string loop. But, when we moved to 48" loop, the flax juice seemed relatively trickier to work with than the guar-based juice.
I will explore some more in the dry season to see if there are advantages in low humidity situations.