Chemical printing in 10 minutes

How to print an original postcard in ten minutes

Safe­ty pre­cau­tions

Warn­ing: only un­der adult su­per­vi­sion.


  • sodi­um car­bon­ate;
  • cit­ric acid;
  • am­mo­ni­um iron(III) sul­fate;
  • potas­si­um hex­a­cyano­fer­rate(III);
  • beaker;
  • cot­ton roll;
  • wa­ter­col­or pa­per;
  • neg­a­tive im­age;
  • hair dry­er.

Step-by-step in­struc­tions

Dis­solve sodi­um car­bon­ate, cit­ric acid, am­mo­ni­um iron(III) sul­fate, and potas­si­um hex­a­cyano­fer­rate(III) in wa­ter to cre­ate a light-sen­si­tive mix­ture. Use a cot­ton roll to ap­ply this so­lu­tion to a piece of wa­ter­col­or pa­per, then cov­er the pa­per with a neg­a­tive im­age and set the pa­per and neg­a­tive un­der a lamp. Af­ter 10 min­utes, re­move the neg­a­tive im­age and rinse the pa­per with wa­ter, then dry it with a hair dry­er – you’ve made a cute win­ter post­card!

Process de­scrip­tion

Un­der the in­flu­ence of bright light, the iron(III) ions in the pho­to­sen­si­tive mix­ture be­gin to ac­tive­ly en­ter an ex­cit­ed state. At the same time, they ox­i­dize cit­ric acid ions, re­sult­ing in the for­ma­tion of a com­plex mix­ture of or­gan­ic sub­stances and iron(II) ions, with which potas­si­um hex­a­cyano­fer­rate(III) forms an in­sol­u­ble blue com­pound:

Fe²⁺ + K₃[Fe(CN)₆] → KFe[Fe(CN)₆]↓ + K⁺

This com­pound is firm­ly fixed in the pores of the pa­per, so when rinsed with wa­ter, the blue pat­tern re­mains!

A sim­i­lar ex­per­i­ment is in­clud­ed in the “Cyan­otype” set from the MEL Chem­istry sub­scrip­tion.