Ink Calendar by Oscar Diaz indicated the passing of time by using the natural pace of ink spreading on paper. So it’s actually a sort of self-updating calendar that demonstrates the passing of time rather than simply indicating it.
The ink is absorbed slowly, and the numbers in the calendar are ‘printed’ by filling with ink at the rate of one a day until the end of the month.
The ink colours used are based on the standard D65 ‘colour temperature’ spectrum, with each month having a color related to our perception of the weather on that month. The colours range from shades of green in spring, through red in the summer to dark blue in December.