Internet Version [Naruhodo no Mori] Vol. 13

by Yumiko Mori

---

Vol. 13     December 15th, 1995

Thermotype

Home science experiments for mothers of elementary school children

Toshi's friend comes to play. We decide to do thermotype together.
Thermotype is usually done with fruit juice, but we test various solution we find in our kitchen.

Mom: "At the edge of the sheet you should write down with a pencil which juice you used."
Toshi: "I am going to write my name too."
Tae: "Mom, where does this strange smell come from?"
Mom: "It's from a throat spray."
Tae: "Do you mean we test that throat spray?"
Mom: "Before we sprayed this to rice and it tuned to purple color. So I want to test this what's going to happen."

While we wait until drawings get dry, we have snack.

Tae: "Pictures start coming out!"
Toshi: "Oh, no! Mine got over-burned."
Mom: "Lemon juice made the darkest color among them."
Tae: "What happened to throat spray?"
Toshi: "It's dry. But I can see something where we drew. It may not work. "
"It's white after baked. Throat spray is different, Mom! "

How to do thermotype

Materials

• Various freshly squeezed juice
  (for example, orange, lemon, apple, and tomato)
  juice from stores (orange, apple, etc.)
  Milk and sugar

  For each item, two tablespoon is sufficient.
  It's fine to have just one kind of juice. You may want to test something other than listed above.
  But you should want avoid something toxic.

• Cups or dishes (as many as juice types)
  

• Several brushes
  (the most convenient if there are as many brushes as the juice types.)

• Drawing papers: several

• An oven toaster
  (gas stove if an oven toaster is not available)

• Chop sticks

Methods

1. Cut drawing papers to smaller pieces (small enough to fit in your oven toaster).
   Any shape is OK as long as they fit in.

2. Prepare juice
   For juice, squeeze orange and lemon. For apple, Grate first and then squeeze.

3. Keep these freshly squeezed juice and juice from stores in dishes or cups.
   Write down which juice you have.

4. Draw anything (pictures or letters) on paper pieces with juice of your choice.

5. Dry thoroughly . When you can not see anything on the drawn papers, they are ready.
   When you want to dry faster, use a dryer.

6. Preheat the oven toaster. Bake a paper for ~10 sec. Bake a paper at a time.

7. When a picture appears, take your paper out. Watch out for over burning.

   How quickly drawing appears depends on oven toasters.
   If you want to avoid mesh lines, you may want to do on the gas stove.
   However there is danger to catch fire on the gas stove. Be very careful. Make sure to do in the presence of parents.

• If you want to send a greeting card in this method, you should write down an instruction how to do.

• The reason why fruit juice turns into brown upon baking is due to that organic molecules, such as potassium, acetic acid, or citric acid, make reaction to hydroxyl residue in cellulose (a paper's main component) and then can not retain water any more. A paper is easier to burn if there is not much water.

• Throat spray does not work, because its residue remains when it dry up.

• My reference also suggest similar experiments with diluted sulfuric acid and Cobalt chloride. Interestingly, these turn into black or blue color. Unfortunately it is difficult to obtain these chemicals and it's quite difficult to do at home.

   Thermotype was a popular game in Japan. It even appeared in textbooks. It may be possible that this game will be remembered as a past one. When I was talking to my children about this game, suddenly my childhood memory returned to my mind. Then I wanted my children to listen my experience. I may be very chatty. It is my desire to talk to children about my experience and what I learned. I believe those will be valuable for them. And I think that's my duty as their mother.

---