"Top-secret inks for spies" experiment

How to make an invisible ink message

Do you dream of be­ing a top se­cret agent? Then you should cer­tain­ly know how to read and write en­crypt­ed mes­sages. In our ex­per­i­ment, we’ll show how cun­ning chemists can make in­vis­i­ble ink at home!

Reagents and equip­ment:

  • lemon;
  • milk;
  • bak­ing soda;
  • 3 beakers;
  • 3 brush­es;
  • pa­per;
  • iron.

Step-by-step in­struc­tions

For the ex­per­i­ment, we’ll need 3 small beakers. Pour a lit­tle milk into the first, lemon juice into the sec­ond, and the bak­ing soda so­lu­tion into the third. Then start to write se­cret mes­sages on pa­per. Dip the brush into the first beaker and write with the liq­uid, and then with the liq­uids in the sec­ond and third beakers, leav­ing an in­vis­i­ble mes­sage on the pa­per. Sev­er­al min­utes lat­er the let­ters dry out and the writ­ing on the pa­per be­comes com­plete­ly in­vis­i­ble. To re­veal the mes­sage, we just have to heat up the sheet of pa­per. We pass a heat­ed iron over the sheet of pa­per, and af­ter a while the writ­ing ap­pears in a bright brown col­or.

Pro­cess­es de­scrip­tion

When the sheet of pa­per with in­vis­i­ble ink is heat­ed, the break­down of cit­ric acid, milk and kitchen soda takes place. As a re­sult of these chem­i­cal re­ac­tions, the prod­ucts of their break­down are re­leased, which col­or the pa­per brown, mak­ing the se­cret mes­sage vis­i­ble. This ef­fect can also be ob­served when sug­ar is heat­ed; it melts and turns dark, turn­ing into caramel.

Safe­ty pre­cau­tions

Ob­serve fire safe­ty rules when work­ing with an iron and oth­er heat­ing de­vices.

Warn­ing! Only un­der pro­fes­sion­al su­per­vi­sion.