How Magna Doodle Works


The Magna Doodle... For kids, it's a cool toy. For parents, it's art without the mess. For the rest of us it's a tribute to the beauty of physics. Discover the science behind the Doodle. See more toy pictures.
2008 HowStuffWorks

In 1974, four engineers from Pilot Pen Corporation invented a "dustless chalkboar­d." Their invention has become one of the most popular drawing toys, with more than 40 million sold since its introduction. Countless children have enjoyed playing and learning with it.

This wonderful invention is the Magna Doodletm!

Toy Image Gallery

In this article, we will take a look inside this fascinating toy and see how it works.

Inside a Magna Doodle

The Magna Doodle is basically a magnetic drawing board. It has the following pieces:

  • White plastic display screen (magnetophoretic display) - what you write on
  • Pen or stylus with a magnet at the tip - what you write with
  • String attached to the pen - holds the pen to the Magna Doodle
  • Long, thin, sliding magnet behind the screen - what you erase with
  • Plastic case - holds everything together and gives you a carrying handle and pen holder

To work the Magna Doodle, you write something on the surface with the magnetic pen. When you want to erase what you have written, slide the sliding magnet to one side or the other (it works in both directions).

Now, let's look at the pieces in more detail.

The Heart of It All

Magnetophoretic display
Magnetophoretic display

The magnetophoretic display panel is what makes the Magna Doodle unique.

This magnetic display has the following structure:

  • Front - A piece of transparent or semi-transparent plastic
  • Middle - A honeycombed or hexagonal plastic lattice
  • Back - A piece of transparent or semi-transparent plastic
Close-up of the honeycombed structure of the display

The walls of the middle, honeycombed lattice are less than 0.02 inches (0.5 mm) thick. Each cell of the lattice is filled with a thick liquid suspension or dispersion medium filled with tiny magnetic particles. The liquid dispersion medium is designed so that the particles can be pulled through the liquid in response to magnetic force applied by the pen or eraser, but they will not change their position (float or sink) due to gravity. To do this, the liquid has special properties:

  • The liquid is thick - This prevents the magnetic particles from sinking, so what you have written stays at the front of the display over time. The liquid is water, glycol or organic solvent/oil-based, and has particulate thickeners: waxes - olefinic polymer, olefinic copolymer, wax fatty acid derivatives - fatty acid amide, dextrin fatty acid ester metal soap
  • The magnetic particles are dark, small and fine (about 10 microns) - This allows them to be seen easily, to stack up and to be nearly unaffected by gravity. magnetic oxides - black magnetite, gamma-hematite, chromium oxide, ferrite magnetic alloys - iron, cobalt, nickel
  • Dye is mixed in - This provides high contrast to the dark magnetic particles. white pigment - most effective (concentrations of 3 to 10 percent) and most commonly used colored pigments - in some Magna Doodles

The middle layer is latticed so that there is always an even distribution of the magnetic particles across the entire surface of the display.

Now that we have seen the display, let's look at the pen.

Magnetic Pen

The magnetic pen
The magnetic pen

The magnetic pen is simply a piece of plastic with a small magnet in the tip. The field of the magnetic pen is strong enough to penetrate the plastic and pull the particles through the thick liquid.

The tip of the magnetic pen

The magnetic pen is ergonomically styled so that anyone, especially little children, can grip it comfortably. The pen is usually tied to the Magna Doodle by an attached string. Some Magna Doodles also come with "shape stampers," which are simply magnets in shapes like diamonds, triangles and circles.

Writing is but one use of the Magna Doodle. You must also be able to erase it, so let's look at the eraser.

Magnetic Eraser

Magnetic eraser
Magnetic eraser

The magnetic eraser consists of a bar magnet in a plastic slider.

Bar magnet and plastic slider

The magnetic eraser sits in the back of the Magna Doodle behind the display, and it can't be seen from the front. The eraser fits in a groove on the case that allows it to slide freely from one side to the other.

Now let's look at the final component: the case.

The Case

The plastic case holds everything together.

It has two pieces:

A front piece that:

  • provides a flat surface for the display (the display screen is glued to the front side)
  • has the molded magnetic pen holder
  • in the case of a Travel Magna Doodle, has a handle
  • in some cases, has holders for shaped magnets (circles, squares, stars)
Back view of the case's front piece showing the back of the display and the magnetic eraser

A raised back piece that:

  • provides a flat, even surface to hold the display and to slide the eraser magnet smoothly and evenly across the back of the display
  • has the molded groove through which the magnetic eraser slides
Front view of the case's back piece showing the raised surface for the display and the groove for the magnetic eraser

Now that we have seen each part, let's see how the Magna Doodle works!

In Action

Back view of a clean display
Back view of a clean display

Let's slide the magnetic eraser across the Magna Doodle and start with a clean display. The front of the display is blank (white), and the back has all the particles. They were pulled to the back by the magnetic eraser.

If you look closer at each cell, you will see that the magnetic eraser has aligned the particles to one side!

Close-up view of the cells from the back of the cleaned display: Note that the magnetic particles are aligned to one side (the direction of the sweep).

Now, if you move the magnetic pen along the display, the magnet on the pen pulls the tiny particles away from the back side to the front side, forming a line. Note that the magnet pulls particles from adjacent cells and aligns them in the direction of motion (in this case, to the right).

Close-up of a drawn line as seen from the front of the display
Close-up of the same drawn line as seen from the back of the display

Because the particles are light and the liquid dispersion medium is thick, gravity will not pull the particles forming the lines back to the other side. What is written will remain undisturbed.

To erase the display, slide the magnetic eraser across the back of the display. As this is done, the magnetic eraser pulls the particles forming the lines from the front side to the back side and aligns them in the direction of the motion. The thickness of the liquid dispersion medium prevents them from floating to the surface, so the front side remains clean.

Erasing the Magna Doodle

The Magna Doodle is a wonderful toy that allows children (of all ages) to draw and re-draw pictures and words without wasting paper or creating chalk dust. When traveling in a car on a long trip, one can draw for hours without creating lots of trash or having to sharpen pencils. Magna Doodles have been used by teachers to help students practice writing and learn words. Magna Doodles have been used in some unexpected places, too:

  • Some sports coaches have used them on the sidelines to outline plays for their athletes.
  • Because Magna Doodles are self-contained, they can be used underwater by divers to communicate.

There are many creative ways to use this wonderful toy. For lots more information, check out the links on the next page.

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