# Scratch Holograms!

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## Introduction: Scratch Holograms!

Have you ever noticed ghostly blobs floating above your black car hood on a sunny day? These blobs are scratch holograms! They appear when the sun is reflecting off circular scratches from activities like washing, polishing, or drying your car. They seem to float because each of your eyes sees the suns reflection at a different point, creating a 3D stereo pair.

'This Instructable has two parts:

Part 1: how to make scratch holograms with a compass

Part 2: how to make a device to draw scratch holograms

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## Step 1: Use a Compass to Make a Simple Demo

Let's start off with an experiment. Find a compass with sharp points at both tips (a drafting compass works well). Adjust the compass to about 2" between the tips.

Find a piece of plastic. I use 1/4" black acrylic (polycarbonate and styrene work fine also). The jewel case from a CD works fine but try to find one with a black CD holder insert because the hologram shows up better with a black background. The best scratches are barely visible and don't produce flakes of plastic. Double stick tape will hold the plastic to your working surface.

With the compass slightly angles, gently scratch an arc. Adjust the compass to a different radius, use the same center point, and make another scratch. In the image, I scratched an arc every 1/8" from a radius of 1.5" to 5.5".

## Step 2: Experiment With Scratch Holograms

Bring the plastic outside on a sunny day, hold it horizontal, and see how the sun reflects off of your scratches. Experiment with turning the plastic. Can you make the image appear and disappear? If you used the same center point, you will see a straight 3D line composed of one small dot for every scratch. Do the larger radius scratches pop higher above the plastic?

Try closing one eye and holding a finger next to one spot of light. Now close the other eye and notice the distance between the spot and your finger. Did you notice that the spots on the larger scratches are further apart? These two spots are the "Stereo Pairs" that are creating the 3D image.

If you saw the spot in the same location with both eyes, it would appear to be on the surface of the plastic. Your brain uses the differences between the two images from each eye to judge depth. Have you ever held your finger in front of you and noticed how its position seems to change as you blink your eyes?

## Step 3: Make a Scratch Hologram Machine!

Let's talk turkey. I've been working on a way to make the process of drawing scratch holograms easier.

This is what you'll need:

Plastic - 1/4" thick black acrylic is show, but CD cases work fine (use with a black background)
Dremel tool (variable speed is better)
Plastic guard that comes in the Dremel 565 Multipurpose Cutting Kit
Drum sanding bit
Pins
Pliers
Dry erase markers
Felt with sticky side (optional)
double stick tape

## Step 4: Start Poking Pins

Disassemble the drum sanding bit and poke a pin into the hole in the rubber part at a 45 degree angle. Use a set of pliers to pull the pointy end of the pin until the head is against the inside of the hole.

## Step 5: Poke Another Pin

Poke another pin in the opposite side of the rubber part, so the part is symmetrical. It helps to bend the pins in the clockwise direction (looking down at the tips of the needles). Reassemble the bit.

## Step 6: Put Felt on the Dremel Guard (optional Step)

The Dremel guard was making small scratches in the acrylic, so I put a ring of felt on the surface. This is an optional step that you might want to ignore if you're not scratching the plastic.

If you want to eliminate two overlapping holograms, cut half of the felt as shown in the last photo. This will tilt the tool slightly, so you will scratch arcs rather than complete circles.

## Step 7: Assemble the Tool

Assemble the tool. Adjust the guard so the tips of the pins are sticking out as little as possible (try from 1/16" to 1/8"). I put a mark on the plastic guard, to help me trace words on the plastic.

## Step 8: Prepare Artwork

Use a dry erase marker to write or draw on the plastic. Straight lines are difficult. Remember to leave at least 1.5 inches around the border. A little double stick tape will keep it from moving around.

## Step 9: Start Drawing

I recommend writing on CD cases first, so you're not wasting money on plastic. Write or draw about one inch above the center of the case to compensate for the radius of the guard. Wear safety glasses (I haven't broken a pin yet, but it might happen). Turn the Dremel to its lowest speed (mine starts at about 3,000rpm). Trace your artwork with the mark on the guard.

## Step 10: Test the Hologram

Test the hologram. A sunny day works best, but you can also get results from a very small bright light. I used a 50W halogen. A Mag Lite Works well if you unscrew the bulb cover.

## Step 11: Collaborate!

My friend Maz-Destruction and I have spent so much time developing this idea. Soon we will try using a hand blender and a coffee grinder.

alphamale@gibbondesign.com

If you are interested in learning more about scratch holography, I strongly recommend the following website.

http://amasci.com/amateur/holo1.html

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## 32 Discussions

To Muffinator: go to your friendly neighborhood Harbor Freight Tools & check out their cheap knockoffs--they work fine.I have one of their flex-shaft tools, and it works great, for not a lot of \$\$\$.

Hmmm... I would love to try that Dremel tool in my CNC router! Converting a drawing to Gcode and then turning it into a hologram...

Great instructable! Years ago I got involved with making laser holograms (big laser, expensive optical table, nasty chemicals). Then I started up again when I read about computer generated holograms (it took all night to calculate a single point with my IBM XT). I've seen the 3-d effect of swirls on a car, but it never occured to me that it was holographic. The presentation that you linked to explained it very well. Thanks!

Hi T3h_Muffinator, You should really buy one of those fancy Dremels, but you can make a scratch hologram device with just about anything that spins. I just posted some other ideas on the last page. Happy Scratching!

Hi, I like your Instructable.  I was wondering if you had any scratch hologram designs plotted.  I figured out the cube, and I just figured out how to do a pyramid.  I figured maybe someone had already figured out some more 3D shapes.   Here is a rough sketch of my pyramid plot.  They should all be squares.  Oh well.  I will try to add dots in between the corners too.
----------------------------------------
|                                              |
|                                              |
|       ________________       |
|      |                               |       |
|      |                               |       |
|      |      __________     |       |
|      |     |                    |    |       |
|      |     |                    |    |       |
|___| __|__________|__|___ |

http://www.eskimo.com/~billb/amateur/holo1.html

I know, I know... It's just that I recently bought a welder for \$200, and I don't think my parents want me spending any more monies on tools for at least two months. Thanks!

Two Months?!?!??? If I bought a welder they would not let me buy things for a year!

if i bought a welder i would have no money to spend on metal to weld... and then would sell the welder to make money... and then would spend the money on metal only to realise that i just sold my welder.

Making a 3D cube is easy.  I don't have a dremel, I just use a compass.  I bought some black acrylic, but I started on CD cases with black backing.  Get a compass with 2 sharp ends.  Scratch a 2x2cm square on the surface, you can scratch deep, this is a guide for one compass point.  Set your compass to 2cm.  Hold one point on the corner of the square and very gently drag your other compass point in an arc across the surface.  Move your guide point over a tiny bit and do another scratch.  The scratches should be very close together, they will overlap in places.  The more scratches the better, you can get very sharp lines if you take the time.  You don't want to scratch deep enough to displace any plastic, just create tiny grooves.  When you are finished with your square, increase the width of your compass a tiny bit and do scratches on just the four corners of the square.  Continue increasing the width of the compass (the depth/height of the hologram) and making scratches from the corners until you have reached 4cm.  Then do a second full square, following the same guide from the first square.  Then go put your hologram on the ground in the sun, in between you and the sun.  If the arcs of the scratches are arcing toward you, you will see the cube sunken beneath the surface.  If you turn it around the cube will float 2 cm above the surface.  All my friends are amazed.  I am trying all kinds of stuff, but I don't know any algebra.

i think those are holographs not holograms cuz holograms are projected in threedee

if you do these right they are 3D. you need algebra equations to make a cube or a tetrahedron etc, but you can do it. these instructions tell you how to make a flat image floating in the plastic, but complex 3D images are possible, too.