Introduction: Thermochromatic Storybook: Invisible Ink

Thermochromatic (heat-sensitive) powder can be mixed into glosses, paints, and much more. By using thermochromatic-painted letters on regular painted pages of a matching hue (or vice versa, thermochromatic pages with regular painted letters), you can create the impression of invisible ink!

Step 1: Bill of Materials

Bristol (for base paper),

Another type of paper (prepped with thermochromatic paste/paint/powder)

Thermochromatic powder (the color of this should match your desired base color)

Gloss Medium

Modge Podge or glue

Hot Plate or small burner

Copper plate



cutting board

optional: laser cutter

Step 2: Decide on the Words

First, you must know the answers to these questions:

What story will you tell?
What kind of font will you use?
How long will the book be?

Step 3: Paint Prep

Depending on the desired color of your book, create a mixture with a high concentration of thermochromatic powder. I used about a teaspoon of powder mixed in with gloss medium, which was added steadily to create a smooth, liquid consistency.
Spend a long time mixing it. I would not recommended mixing it with water as it dilutes the mixture and will alter your color.
ANY COLOR PAINT you add to this mixture will be visible later. Thermochromatics work by turning transparent when exposed to heat. If you paint orange thermochromatic on yellow paper, you will get yellow in heat and orange at room temp. Keep this in mind.

Step 4: Paper Prep

Lay out your bristol paper, thermochromatic mixture, ruler, and acrylic base paint.
The "base" color I refer to is the color of your pages. To work as invisible ink, the color of your pages must match the color of your thermochromatic mixture as well as possible. The words and letters will still appear as a slight rise on the page if you use the collaging method I did, however, you can choose to carefully paint your thermochromatic words/letters in if you prefer a smoother look.

Paint two coats of your thermochromatic color on your designated paper for your words and letters, and, on your bristol base paper, paint with regular paint in an identical hue. Remember: the paper for your words and letters you've painted with thermochromatics will change color under heat. If the paper is white, the words will become white when heated. If you prep it with yellow acrylic paint, yellow words will appear under heat. The possibilities are as endless as the sky.

Your pages must be able to lie flat within the copper plate when open so that the letters can react. Make sure to size your story accordingly.

Step 5: Testing

Make sure that you haven't made your book so thick it won't react to the hot plate's heat. Test out your book by making sure the front cover still reacts to the heat through the density of all your pages.

Step 6: Lettering

Once your pages are dry, it's time to add letters and illustrations to your pages!

Storyboard and design your book layout now. Make sure you have enough pages prepped.

Decide on your font. You could have something very graphic and illustrative, or a more even, traditional typeface. Handwritten or machine-made, laser-cut or hand-cut (unless you are writing directly on your pages and not collaging). You can make your own font with templates on the internet (shown in pictures). I played with a few fonts and ended up writing my story in cursive, scanning it, and creating an illustrator file so it could be laser-cut. The cursive made gluing much less labor intensive since I had to glue words rather than letter by letter.

If you are cutting out your words/letters by hand, I suggest you put two, pre-thermo-coasted sheets down when cutting out letters so you make two at a time, especially in case your words suffer a tear!

Once cut, paint your letters all around the edges for full-bleed invisibility look. Leaving the edges raw shows a mischievous shadow that will give away the underlying color before the big reveal. This accent can be used to your advantage if you wish.

Step 7: A Note on Laser Cutting

If laser cutting, take note of the strength and speed setting of the laser. Play around with them if your are having troubles getting the laser to cut out your fine lines. The bigger the words, the easier they will be to manage.

Step 8: Assembly

Once your letters are ready, glue them in!
Keep testing to make sure each page works as you want it to.

You can sew your spine together if the form of your book calls for a codex. Mine was page by page, unattached.

Step 9: Final Trim

Lastly, get a ruler and trim the edges of your book with an exacto (this is specifically for codex-style books) to finish off your book with a clean look.

Congratulations on your magic new book!