Why do coloured soaps produce white foam? | Let’s Make Education Simple
We all use different brands of soap for bathing.
But ever wondered why all the soaps despite the difference in colours, can only produce white foam?
Let us discover the science behind it!
When soap in many colours like red, green, and blue, is mixed with water, it gets mixed with the air. When we rub our body surface, including bathing and washing our hands, a lot of small bubbles are formed. These tiny bubbles turn into foam.
Experiment: Why do soaps and handwashing foam white?
When we look through a window from a dark room into a bright room, we can see everything in that room. When our room is bright or during the day, we cannot see anything in the next room; we can only see our reflection.
The reason is that if the neighbouring room is bright, the light from that room enters through the glass window and shows us everything. When we look at the neighbouring room through the glass window during the day, the glass window acts as a mirror for us. So, we can only see our reflection.
Just like bubbles acting as glass windows. There will be less light in these bubbles. Outside the bubbles, the light is extremely bright. When the outside lights contact bubbles, those bubble lights are scattered in the same outside colour. Normally, we are surrounded by only white light. That is why foam is white in colour.
Experiment: Will the foam colour be visible in other colour variations?
In case, if the light outside is pink or yellow in colour, when we look at the foam in a glass tumbler, the bubbles in it will be scattered in the same colour as the outside. That is, the foam appears pink or yellow in colour.
Finally, let’s know one more thing. If more colourants are added in soap or hand wash, the colour of the water changes when we wash, so, fewer colourants are added in soap and hand wash.