Spanish designer Oscar Diaz has designed a calendar that uses the capillary action of ink spreading across paper to display the date.
In his own words, although not brilliant English: "The ink is absorbed slowly, and the numbers in the calendar are "printed" daily. One a day, they are filled with ink until the end of the month. A calendar self-updated, which enhances the perception of time passing and not only signaling it.
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.
The scale for measuring the “color temperature” that I have used is a standard called ‘D65’ and corresponds roughly to a midday sun in Western / Northern Europe.
The "Ink Calendar" was developed for “Gradual “, an exhibition featuring works, which were evolving during the exhibition time at the London Design Festival 2007."
Oscar Diaz's Site