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Experiment: How to make invisible inks from a lemon, milk and baking soda

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Published on 15 Mar 2019 / In Film & Animation

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

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.

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