Although it’s intriguing to imagine the peppermint strips neatly wound inside the tube, actually the stripes don’t go onto the paste until it’s on its way out. A small hollow tube, with slots running lengthwise, extends from the neck of the toothpaste tube back into the interior a small distance. When the toothpaste tube is filled, red paste- the striping material- is inserted first, thus filling the conical area around the hollow tube at the front. (It must not, however, reach beyond the point to which the hollow tube extends into the toothpaste tube.) The remainder of the dispenser is filled with the familiar old white stuff. When you squeeze the toothpaste tube, pressure is applied to the white paste, which in turn presses on the red paste at the head of the tube. The red then passes through the slots and onto the white, which is moving through the inserted tube- and which emerges with five red strips.
From: How Do They Do That? by Caroline Sutton
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