The Magic Cloth

For a related classroom activity, see Color Analyzers.


1. See Lights to Fill the Planetarium with Color in Filters

2. Special-pattern “Magic” Cloth

A paper version of the magic cloth can be printed in color from the master at the end of this Materials section, then duplicate color copies, one for every one or two people in the audience (two can share easily). For durability, copy on cardstock. In the original version of the show, we used lengths of cloth, each about 18" wide and 24 feet long. The fabric has a pattern with colors shown in drawing at left. When viewed with a red filter, the zig-zag stripes seem to disappear “magically” because they blend in with the color of the stripes they are on. The exact pattern of cloth is not important as long as some dramatic “disappearance” of a color in the fabric occurs with one of the color filters of the color analyzer. It is fun to take color filters to a fabric store and view various fabrics through the filters until one with a suitable dramatic effect is found. You may also find suitable patterns in gift wrapping papers or decorative paper plates.

Presenter's Script

Now, let’s go back to a red star and examine a piece of cloth (or color pattern on paper). Space travellers call it “the mystery cloth” because they have a hard time agreeing on the colors they see on it.

Make sure only the red light is on. While you talk, start unrolling the multicolored cloth or handing out paper color patterns so that everyone will have it in front of them. With rolled up cloth, once you start, let the audience continue unrolling it.

Will someone please describe the pattern on this cloth for us? [Stripes of the same width; colors.] Does everyone agree with that description? [Accept a few opinions.]

Perhaps we can agree that there is a bright stripe that reflects red light (or looks bright under red light) and a dark stripe (or two) that absorbs it (or looks dark under red light).

Let’s take the cloth to a different star, a green star perhaps, to see if we can get some more information about the colors of this cloth. Please fasten your safety belts again.

Red lights off; on green lights. Expect gasps of astonishment from your students.

Wow! What happened!!? Could this be the same piece of cloth?

Would someone please describe this new pattern for us? [There’s a new thin zig-zag line, so there are three stripes of different widths. Colors?] Does everyone agree with this new description? [Listen again to a few opinions.]

We want to discover the true colors of each of those stripes, and to do this we can use what we learned when we looked at our clothes under different color lights.

Does that zig-zag look bright or dark? [Dark.] That is because it must be absorbing the green light.

Is it possible that the zig-zag could be green? [No. If so, it would look bright.] What about the background stripe that the zig-zag is on, does it look bright or dark? [Bright.]

It looks bright because it is reflecting the green light.

Is it possible that the background could be green? [Yes.] Could it be another color? [White.]

Now keep track of that zig-zag by putting your finger on it while we return to the red star to see what happens.

Turn green light off; red light on.

The zig-zag disappeared! Where did it go? I told you to keep track of it!!

Now, does the area where the zig-zag is supposed to be look bright or dark? [Bright.]

The zig-zag and its background are two different colors but they are reflecting red light equally.

Is it possible the zig-zag could be red? [Yes.]

Now its background looks bright, too.

Could it be red, also? [No.]

It looks bright with both red & green, so it probably is white, yellow, or some other color that reflects both red and green. Now, put your finger on the dark stripe.

Could this be red? [No, because it absorbs red light.]

Let’s go to a green star.

Red light off, green light on.

The stripe looks bright.

What color do you think it could be? [Green; or maybe, blue.]

If it is blue it should look brighter near a blue star: let’s see.

Green light off, blue light on.

It looks darker, therefore it’s not blue, it’s probably green. So far we have guessed a wide green stripe, and a red zig-zag on a white or yellow background.

What color light do you think we could shine on the cloth to see its real colors?

If they say: red, blue, green, respond: “We already looked at it with those colors.” When they say any other color: “I only have red, blue and green.” When they suggest white or a combination...

Let’s see what happens when we combine colors. Look at the ceiling as I mix the colors: We have blue light, now we add green.

Green light on.

We get aqua (or turquoise, cyan, or plain blue-green). Let’s add red to blue.

Green light off. Red light on.

We get pink (or purple, or magenta). Let’s add green to red.

Blue light off. Green light on.

We get yellow! (This is usually a surprise for most people.) And finally let’s have red, green and blue together.

Blue light on.

We get nearly WHITE!! White light is made from all colors mixed together. Look at your clothes now.

Do they look their normal color again? [Yes.]

Now we can see the “true” colors of the cloth and we find that we were correct in our guesses.

Please roll-up the cloth that is not-so-mysterious anymore.

Collect cloth once it is rolled up. Turn on red light only.

In summary, we can say that an object looks brightest when illuminated by light of the same or nearly the same color (because the object reflects the light), and looks dark when illuminated by a light of very different color (because the object absorbs the light). Pale colors and white look bright in any color light, and dark colors like black, or brown, look dark in any color light. The red zig-zag and its pale background looked equally bright in the red light. In fact we could not tell they were different and that’s what made the zig-zag disappear. On the other hand, in blue or green light the red became very dark, while the pale background remained bright. This is because light striking an object is either reflected into our eyes, or absorbed. Objects reflect mostly the color light that they appear to be, and absorb all other colors.