This is an art experiment.
Cyanotype is an early photographic printing process, first discovered in 1842 and still used today for blueprints. Your postcard is a future cyanotype print, coated in a safe, non-toxic, light-sensitive chemical solution. This solution reacts with UV light to make a blue image.
The postcard will capture a visual record of its time in the mail, based on the light it was exposed to in transit. I need your help washing the print to finish the process.
Washing the print
To develop and fix the image, the postcard needs to be rinsed in water. Tap is totally fine.
Fill a flat pan or dish (that you don’t use for food), submerge the card, and gently agitate the water. You can also place the card flat in a sink and rinse it under gentle pressure from a faucet or sprayer. Don’t scrub or spray too hard— the image could be damaged!
The postcard will change from a greenish bronze color to navy blue. Rinse until the water runs clear and any white areas have no trace of yellow or green left. Pat the postcard dry so there aren’t any puddles—they’ll leave spots. Then hang or lay the postcard out to finish drying. Hanging prints on a range hood with a magnet works well if you have one.
The print will darken to a deep blue over the next 24 hours or so. Once it’s fully dry, either send a photo or mail the postcard back. I’ll post them here with their city-to-city route and date.