Bath bomb
A bath bomb is a hard-packed mixture of chemicals which effervesces when wet. They are also used to add scent and colour to bathwater. They are a form of bath fizzies.
Composition
Bath bombs' primary ingredients are a weak acid and a bicarbonate base. These are unreactive when dry, but react vigorously when dissolved in water to produce their characteristic fizzing over a period of several minutes; carbon dioxide bubbles on bathers' skin gives a tickling sensation some find pleasant. A common chemical mixture is citric acid and sodium bicarbonate:
The other ingredients in bath bombs can vary considerably. Most have scented ingredients — such as essential oils — in their composition to impart a pleasant fragrance to the water, and some are brightly coloured. Solid objects, such as glitter, can be added. In Japan, there are usually bath balls, often called Bikkuri Tamago (びっくりたまご lit. "Surprise Egg") The difference between other bath bombs and Japanese bath bombs is that when the ball is fully dissolved, a small object is revealed. This is usually a figure. There are many anime bath balls in Japan.
Production
Bath bombs are generally spherical but can be found in a variety of shapes, such as tablets or lumps. Shops offer a wide range of bombs, but they can also be made at home.