| 摘要 |
A coaster of this invention comprises an upper sheet having transparency and permeability, a printed sheet provided with a color-changing area of which surfaces faces the upper sheet, and a color former for changing the color-changing area. The color-changing area is printed by an ink containing a color-changing agent which changes from substantially invisible colorless state to a visible color state by applying a color former. The color former is set in the coaster such a way that the color former can melt out for applying to the color-changing agent by means of water permeating through the upper sheet.
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