Holiday cards aren't usually this transparent. If you send a picture with your dog, will your parents think/know you're desperately single? If you take a cutesy picture with a boyfriend or girlfriend, will your middle school bully wish he had given you harder wedgies? Now with these cards printed on transparencies, they'll probably all just think you don't have enough to do in your 9-5. :)

Time to blow some minds with color this holiday season. With your holiday card pigment puzzles, you can make cards that come off the fridge to ratchet up the science in your winter celebration.

These cards work by dividing up a photo into its pigment elements Cyan, Magenta, Yellow, BlacK and scrambling them across several images. When four cards are combined and held up to the light, you can see the original image again. It's just wonderful.

What: Holiday Card Pigment Puzzle!
Why: Because your aunt is either going to love 'em or hate 'em.
Concepts: color, pigments, optics, light, art, joy
Time: ~ 20 minutes on computer, printing and cutting vary by number
Cost: ~$0.20-$0.75 per card depending on size
Materials:
- Photoshop or GIMP (these instructions are for Photoshop, they have free trials)
- Transparencies (for Laserprint is what I used, you can do Inkjet too)
- Color Printer
- Cutting device
Extra Resources: To learn about the pigments and light in this process, check out the Teacher Institute.

Let's get coloring!

Step 1: A Video for Video Learners!

Here's a significantly long video on how to do the computer portion of this project. This is for people who learn best by video. It is guaranteed to not be entertaining but informative if you like following along. Of course skip through to parts that feel like review for you.

Otherwise, proceed to the photoshop steps! Don't worry, it's not too tricky!

Step 2: Photoshop: Divide Image in to Pigments

Okay, let's Photoshop!

1. The first step is to get your image on to a single layer. If you have multiple layers, select them all and Hit 'Command+E.'

2. Then go to Image > Mode > CMYK Color, and click through to accept changes.

3. Now you can go to the channels tab and see your image separated into CMYK layers represented by black and white image.

4. Click on the menu in the channels tab and select 'Split Channels.' This is not reversible. You should now see four documents, each labeled for its respective pigment.

Step 3: Photoshop: Add the Colors

So now your image looks like a bunch of black and white images, but we want color!

1. Start with the Cyan image, and click Image > Mode > Duotone.

2. Click 'Monotone,' and click on the color palette.

3. In the grid of options for colors, look to the right where they have the CMYK options. Set C to 100% and 0 for MYK. You should now have an all cyan image you can save to the desktop.

4. Now repeat for the Magenta, Yellow, and Black layers but instead of setting C to 100%, set the respective pigment to 100% and 0 for the others.

If you just want CMYK holiday cards without the grid, you can go ahead and print from here!

Step 4: Photoshop: Make Guide Rectangles

To speed up the grid process, let's make some guides that will help us sample quickly.

1. Start by importing all four color layers to a new image document.

2. Make a new layer, and select the upper left quadrant of your image. Hit 'Command+I' to select the inverse, and fill it in with the paint bucket tool.

3. Make new layers and repeat for the other four quadrants.

Step 5: Photoshop: Make the Color Grids

Now we'll make the four different cards to combine.

1. Start by selecting the upper left quadrant from the first guide you made. Then click on the Cyan layer. Hit 'Command+C' and 'Command+V' to copy and paste. You should see a new layer with the upper left quadrant of the cyan layer.

2. Go around the grid doing the same for each color, so you have one quadrant of each.

3. Once you have a complete grid, save it to the desktop. Then repeat the process but advancing where each of the pigments are one quadrant clockwise. Do this for four total cards so each quadrant will have each pigment between them all.

Step 6: Print and Cut

Oh we're getting there!

Simply print however you wish (you can tile if you want them smaller), and then cut out using scissors or a cropping device. Depending on your audience, you can add a guide to line them up in Photoshop or just let them at it.

One thing to be aware of is transparencies can be a little funky in a lot of printers. Make sure you have the right printer for the type of transparency (laser vs. ink), and see if there's a transparency setting. On some, you may have to load them one at a time to keep them from sticking together.

Crop them and then put one card of each type to make sets of four to give!

Step 7: Light! Cards! Action!

You did it! You can line up all four and hold them to a light, the sky, or a light box to see the magic. You can go way beyond holiday cards, and make anything you so please.

I'm excited to see your creations and the colorful mirth you send out. Share them, comments, or questions below! I'm happy to help. :)

If you want to check out some of the science of the pigmentation and color let through, check out the Teacher Institute at the Exploratorium for a great explanation.

Have a wonderful one, be colorful, and as always, keep exploring.