Why is the white dragon called soap in mah jongg?

Why is the white dragon called soap in mah jongg? People were always turning the tile over to see what was on the other side (revealing to others that the tile was a white dragon). So a rectangular design was added. American players thought the blank tile looked like a bar of soap, so they call this tile “soap” to this day.”

People were always turning the tile over to see what was on the other side (revealing to others that the tile was a white dragon). So a rectangular design was added. American players thought the blank tile looked like a bar of soap, so they call this tile “soap” to this day.”