Make invisible ink with this invisible ink recipe.
Of course this is not the ultimate 1917 CIA ink recipe and you won't have access to this secret before 2020 at the minimum.
Because the CIA is fighting to keep it a secret, maintaining it's agents are still using the formula in their operations around the world. There are people who tried to force the government into making the related files on the subject public. But a judge ordered to keep these files secret until 2020.
In the meantime...
you can make invisible ink with a less sophisticated but still working invisible ink recipe.
* Baking Soda
* A toothpick , fountain pen, or even just a Q-Tip
* A piece of paper
* A source of heat (light bulb etc)
Step 1 - Mix one table spoon of baking Soda to two tablespoon of water. This is your ink solution.
Step 2 - Now take your Q-tip, toothpick or fountain pen and dip it in your solution and write your message on the paper.
Step 3 - Let it dry
Step 4 - Now hold the paper with the secret writing near a light bulb
(or other heat sources). You will soon see the message appear in a brown color.
This invisible ink recipe article is pretty rudimentary compared to the rest of my Spy Equipment Guide, but it is one of the few known " how to make invisible ink " method that is available to the public.