This will be an article about self-closing loops. It is VERY incomplete but is being filled in (late Jan. early Feb 2013).
IntroEditSelf-closing refers to tri-string loops that are light enough that the soap film's surface tension can at least partially close the opening. As a self-closing loop becomes drained of juice during bubble creation, the surface tension can, in some cases, be strong enough to completely close the opening.
Some lightweight absorbent wicks are not self-closing when fully-laden with bubble juice but become somewhat or even highly self-closing when a bubble's formation drains the loop of its juice. This can be very helpful when creating giant bubbles as it provides the bubbler with helpful clues about the time to close the bubble.
Loops are self-closing when the surface tension of the film is stronger than gravitational force on the bottom string. Generally, this happens only with a fairly lightweight bottom-string. Although, there are lightweight strings that are so absorbent that they are not self-closing. There is a wide range of self-closingness possible. Strongly self-closing loops may be difficult to get open at all without some sort of weight (such as washers or split rings). Moderately self-closing loops can be barely self-closing (the sides being bowed barely inward when the loop is initially opened) when freshly dipped yet strongly self-closing when drained of juice by the creation of a large bubble. Weakly self-closing loops will show no tendency towards being self-closing until the loop is nearly entirely drained of juice.
BlowbackEditThe internal pressure of the bubble may keep the loop open with lightweight loops even if you bring the wand tips together. This can happen with lightweight loops even if they aren't self-closing. If the loop is self-closing, when the bubble gets to the "right" size, it will pull itself closed and zip up the loop as it does.