I have had a few sessions the past few weeks that have me rethinking some of what I thought I new about dilutions. When I started investigating higher-dilution mixes (on the order of 25:1 to 50:1), I noted that there was a dramatic improvement in bubble color when using ? water:Dawn Pro dilutions around 25:1 with improvement in longevity little or no impact on size. At the time that I was exploring this (Spring and early Summer 2012), I was mostly using 32"-48" top-string loops with some sessions making use of a 70-75" top-string loop.
Large loops and dilution? Lately, as you may know, I have been exploring much larger loops -- mostly a 100" or so top-string wand as I am not very proficient yet with a 120" top-string.
Recently, I started using HEC-based mixes again -- and have been very impressed with the bubbles that I have created with them (under very good conditions) using the large loops. I have tried creating a high-dilution version of the mix but have not yet managed to create the same long-lived (relatively) super giants with dilutions of 20:1 - 24:1 that I can with a 16:1 dilution.
I am not sure if the problem has been one of luck or if with the very large bubbles there is some benefit to the extra soap. Since I prefer the richer colors of slightly more dilute solutions, I intend to see if there is some fix for this -- either an adjustment of the amount of polymer or perhaps the use of secondary and/or tertiary polymers.
So far, in every session where I started with a 24:1 or so mix, it has improved by adding one or two tablespoons of Dawn Pro per liter of solution. But, perhaps, it is just a matter of getting the polymer levels right at this dilution. Years have gone into recipes in the "standard" dilution range (let's call that anything under about 17:1). 20:1 and higher have not been as widely explored. So, it might just be a matter of discovering the right balance of ingredients.
.....Ghosts/PEO/Sodium Citrate. On a completely different note, I mixed up some eGoo the other day and diluted it 16:1 (water:concentrate which yields about 25:1 water:detergent) and added about 1 gram sodium citrate dihydrate (some food grade stuff that I have had around for awhile as a cooking ingredient). I tried it today (11/25/2012) with a really big loop (100" top-string) with 52F and about 85-90% humidity. I noticed some odd things: bubbles popped with a whoosh, and the bubbles were virtually ghostless! I have never seen this with PEO mixes (except when Mr. Bubbles was mixed in). I need to do some head-to-head comparisons to see if it was the chemistry or the conditions!