Thermochromic Imaging

This instructable is part of my thesis project using thermochromic pigment to silkscreen receipts.  The use of the pigment is to portray an image of a subject on the back of the receipt, over narrative text.  The idea is that when the image of the subject is touched, the image fades and a quote from their narrative is revealed underneath. This interaction allows one to have an immediate and subtle understanding of the subject encountered through the existing artifact (the receipt) collected everyday.

The first step is to clamp your screen down on the table. Make it tight so that the screen may be lifted like a cover over the table.  Tape over the immediate parts that you do not want to screen, leaving the part you want to print exposed.  In this case, we start with the text that will be underneath the photo.  

Next line up your paper where you think it should be placed under the screen.  You can put the screen down over the paper to eye where it should be placed. When you have it where you want it, place tape to mark the edges of the paper so that you have a consistent edge to place your blank pages for multiple prints.  It may take some trials to get the paper positioned correctly.  Have newsprint handy to test out your prints before you use your good paper!

Now to get the ink ready for the text.  I used about a half cup of silkscreen base with a half teaspoon of black ink.  Add a drop each of reducer and retarder and mix well.

With your screen down over the paper, blob pour the ink mixture below the exposed text.  Using your squeegee, pull flood the ink to the top of the screen.  Then push stroke hard and consistently down the screen to make your print.  Then pull flood the remaining ink back to the top of the screen for the next print.  

Lift your screen to see your text printed.  Do not reprint because it will not be a crisp print for the text.  If it didn't come out right, try again with a new piece of paper.

Repeat Steps 1 & 2 for exposing the image on the screen for printing.  This is the layer that will go over the text.  

Now for the key moment:  For the heat sensitive image, I mixed a half cup of silkscreen base with two tablespoons of black thermochromic pigment.  Do not add ink if you want it to fade clear when touching the print.  Mix the base and pigment with a drop of reducer and retarder.

Repeat Step 4 with the pigment mixture over the image.