How Did a Little Soapy Water Fill a Courtyard with Rainbow Bubbles?

From the late 1960s to the early 1980s, children in some parts of China could play with bubbles without a bottled solution. A common method was to scrape a little laundry soap into an old bowl or enamel mug, add water gradually, then dip a piece of straw, thin bamboo or an empty ballpoint-pen tube into it. Materials and names varied by place and household; this was one recurring homemade method, not a universal childhood experience.

The hard part was not blowing but adjusting the water until it would hold a film. With too little soap, only a ring of water clung to the tube and burst as soon as it swelled. Too much could make the mixture thick without making it lively. Children added water or soap, testing whether a thin sheet would span the opening. Once it worked, they began with a stable small bubble, then compared size or distance before it landed. One child mixed, another found a suitable tube, and each waited for a turn. Observation and patience became part of the game.

The colours did not come from dye. When light reflected from the two surfaces of the very thin film, variations in thickness strengthened some colours and weakened others. Children might not have known the term thin-film interference, but they could watch the colours flow downwards until the top darkened and burst. Almost nothing of the toy could be kept: wind, dust and drying destroyed it. Its pleasure lay in the temporary process of tuning ordinary materials until repeated failures finally floated away. Children should blow outwards only and never draw the soapy liquid into the mouth.