(Update March 20, 2014) I just spent a few minutes investigating. I gradually added salt to a 20:1 (water:detergent ratio) guar juice that had been fortified with PEO. Over the course of 10 minutes, I gradually added salt until 30 grams salt had been added to 2 liters of bubble juice with no infuence on the ghosting. This was pH-adjusted juice unlike the juice in the original session. It seems pretty certain that the high pH (or alkalinity) of the juice in the original session was responsible -- something I had not realized until after I had made the bubbles.
ORIGINAL ENTRY: Does salt (sodium chloride) disrupt ghosting of detergens that normally ghost? It seems like that might be the case. Although, I have only a single anecdote so far -- and not time at the moment to follow-up. (NOTE (added later that afternoon): upon reflection, it seems likely that the ghost disruption was due to high pH -- already known to disrupt ghosts -- and not the salt in the mix, but I will follow-up.)
I spent a little time today (78F and 30% humidity) making bubbles with my 5 year-old son and his friend. The only solution on hand was mixed up from a guar/salt/isopropyl/Dawn Pro solution. I was surprised that there was almost no ghosting. The bubbles popped into a cloud of large droplets (not Charmy's vapor-pop). I added a little PEO to see if that made a difference -- but no, we got the same results. It is possible that the salt was not responsible. It might be that the pH of this solution was higher than usual (and we have seen that ghosting and pH are correlated --- though when the pH is high enough to disrupt ghosting it also tends to result in poorer performance).
Back story...
Though I have not had time to make bubbles or do much experimentation lately, I have been revisiting some attempts to make guar-based bubble concentrates. When there is not enough water present, the guar gum tends to fall out of solution. Oftentimes, an insoluble gel disc forms. This makes it difficult to make a concentrate that has both good shelf life and is concentrated enough to be worth the effort.
One area of experimentation has been adding ingredients that might interfere with hydration. So far, it has seemed that it takes only a bit of detergent to render a water/guar solution (even one that is not terribly concentrated) unstable. So, a nice uniform guar, water, detergent mix that is akin to something like eGoo has been very elusive. In the waterless concentrate explorations of 2012, there were some near misses. Solutions where the guar did not form a discrete insolube disk. These are more slurry than nice concentrate. But, they would still be convenient.
One line of exploration has been to use salt in the concentrate to see if it disrupts hydration by making the water less available. It seems to work to an extent.
My son and his friend wanted to make bubbles. I didn't have any solution handy. So, I grabbed a bottle of the concentrate and diluted it. I was very surprised that the resulting bubbles were virtually ghostless.
As I write, I realize that this batch of concentrate had no pH adjustment. So, it could very well be that the pH is high enough to be responsible.
I will follow up when I have time....