How do toothpaste makers get the stripes in toothpaste? And why do they persist until the tube is used up?
• This is one of those simple inventions that has been helping manufacturers to sell toothpaste for decades. We have to go back almost 50 years to find US patent number 2,789,731 and UK patent 813,514, both in the name of Leonard Lawrence Marraffino. He licensed his invention of striped toothpaste to Unilever, and this company subsequently marketed the first commercial version, which was called Signal in the UK. When the tube was squeezed it produced red stripes on white toothpaste.
Behind the nozzle was a hollow pipe that extended a little way back into the toothpaste tube. The white paste travelled down this pipe. Around this pipe was the funnel-shaped neck of the tube and, at the narrow end of this, the pipe had tiny holes that opened into its interior. When filling the tube, red paste was first squirted into the funnel-shaped neck until just shy of the rear entrance of the pipe. Then the white toothpaste was added, and the end of the tube sealed.
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When you squeezed the tube, the white paste flowed out through the pipe, but it also compressed the red paste, forcing it through the tiny holes to form the stripes. If the stripes stopped coming out, they could sometimes be made to start again by warming the toothpaste tube in hot water.
Colgate-Palmolive’s US patent number 4,969,767, granted in 1990, describes a scheme for adding stripes of two colours. Here, the central pipe is surrounded by a wider but shorter pipe, which creates a space for a second coloured paste. Tiny holes, once again, deliver this paste onto the surface of the white paste.
Tom Jackson, Silloth, Cumbria, UK
• Another way to create striped toothpaste is to pack columns of different coloured pastes side by side in a vertical dispenser. The pattern is reasonably well preserved even when its diameter is reduced as the pastes are forced through the hole at the top of the tube. However, unless you use a pump dispenser, the action of squeezing the tube tends to mix up the stripes.
Neil Rashbrook, Stevenage, Hertfordshire, UK
• Thanks to Blair Scott of Falkirk, UK, for spotting an interactive demonstration of pump dispensers being filled using this latter method: . Patents of the inventions mentioned by our first correspondent, complete with diagrams, can be found at – Ed