Low-Tech Communications Post-IHTF/Invisible Ink! Part 3

Low-Tech Communications Post-IHTF

Invisible Ink! 

Part 3

By servantheart, Editor at Large


In Part 1 we talked about how to make sympathetic (disappearing/invisible) ink that is red in color, and in Part 2 we talked about how to make ink that is blue in color for writing “secret” messages. Today, let’s do “black”! Here are chemicals that will produce a black color for sympathetic (invisible or disappearing) “ink”:

  1. Write with a solution of one part sulfuric acid mixed with 10 parts water. Writing disappears, but reappears when it is gently heated.

Note: this is a dangerous substance. There probably are safer choices than sulfuric acid. Sulfuric acid (sometimes spelled “sulphuric acid”) is highly corrosive as a mineral acid. It has the molecular formula H2SO4. It does have a pungent odor (serves as a good “warning”, sort of like a poisonous plant); it is generally colorless but may have a slightly yellow look when dissolved in aqueous solutions. Some labs dye it dark brown to alert people to “hazard” for this chemical. The historical name of sulfuric acid is oil of vitriol.

  1. Write with a 15% solution of ammonium hyperchlorate. Heat the paper carefully to develop the writing.  I am having trouble finding info on ammonium hyperchlorate, so, do your homework and proceed with caution.
  1. Dissolve 20 grains of iron sulfate in one ounce of water. Develop the writing by  sponging with a solution of 5 grains of tannic acid dissolved in one ounce of water.

Tannic acid should not be confused with tannin, found in both green and black teas. Tannic acid is a specific commercial form of tannin, a type of polyphenol; these two are NOT the same chemical compounds. Commercial tannic acid is generally extracted from certain plants, however, including tara pods, gallnuts, or Sicilian Sumac leaves.

  1. Starch boiled in water will turn black when treated with tincture of iodine. These two are very common, inexpensive, and may be one of your best “hidden” choices – who would put these together as an “OpSec tool”, for example?


  1. Writing with a strong solution of mercurous nitrate then exposing to ammonia fumes will cause black writing to appear. On the other hand, exposure to ammonia fumes might me turn black, as well!

Clearly, if you’re going to experiment with some of these chemicals, you might want to do it outdoors, for your own ease of breathing and ease of mind. And be very careful how you store this stuff!

So, what if you’re not exactly the chemistry/geek type, but you want to try some fun stuff like this? Well, look in your kitchen! Use the juices of some of these food items and apply mild heat to reactivate them, after drying:

Lemon juice/Leek juice/Milk/Buttermilk/onion juice/cabbage juice/artichoke juice/grapefruit juice

Salt Writing: dissolve common table salt (sodium chloride) in water (they do not give ratios). Write with this solution on white paper using a clean pen (I’m sure they were using “nibs” or metal point pens such as one would dip in ink – you can buy them in hobby stores, in the “Italic writing” sections). When the writing is dry, scratch over it with a soft pencil and the words you have written will show up plainly in dark lines.


DO keep in mind that this book was written at a time when paper was simply paper; today, most papers are “specialized” and many have any number of chemical treatments, including intentional chemical coatings. This probably will significantly impact your results. I’m guessing the cheaper paper has fewer chemical treatments – just a hint. Experiment, and have fun along the way!

Lippy and Palder’s book, “Modern Chemical Magic” will also teach you how to write invisibly (sympathetic inks) with the colors green, brown, violet, and yellow. It contains many “magic tricks” using these compounds, such as the trick known as “spirit writing”. The book is paperback, yet, it HAS NO COPYRIGHT – not that I can find, anyway. Can you believe that? It does come with a forward by the famous magician, Harry Blackstone. The authors’ complete names are John D. Lippy, Jr. and Edward L. Palder, though I’ll be surprised if you can the book.

And now that we’ve talked about ways to use “sympathetic” (invisible) inks, what ideas and/or suggestions have you come up with to maintain OpSec in low-tech communications post-IHTF?

We want to hear from you!

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