Spanish designer Oscar Diaz has designed a calendar that uses the capillary action of ink spreading across paper to display the date. Every day the ink will "print" a number on the calendar until the end of the month.

The ink colors are based on a spectrum, which relate to a “color temperature scale”, each month having a color related to our perception of the whether on that month. The colors range from dark blue in December to, three shades of green in spring or oranges, red in the summer.

I think Oscar Diaz hasn't made only a calendar but also a piece of art which give you a perception of time passing and not only signalling it.