This Instructable covers how I made two Valentine's Day thaumatropes for my girlfriend instead of a card.
What is a thaumatrope? Here's the wiki article en.wikipedia.org/wiki/Thaumatrope, but basically it's a disc with strings attached. On either side of the disc is an image. By twisting the strings you can make the disc turn over. When the disc turns fast enough the two images merge into one through persistence of vision. It was a popular toy in Victorian times.
Step 1: Gather Your Materials and Tools
You don't need much:
-Nice stiff card
-String or two rubber bands
-A hole punch (you could manage without this, it's just neater)
-Lots of colourful crayons and pens (red is a classic)
-A CD (love songs would be appropriate. I used a linux liveCD)
Step 2: Cut Your Disc and Draw Some Guidelines
Get your nice card and draw a circle using the CD as a template. You could use compasses but the CD is a good size and a lot less fiddly.
Mark the centre of the circle. It doesn't need to be perfect, use the hole in the CD as a rough guide.
Cut the circle out.
Now you have your disc. Using the centre point, rule a straight line across the diameter of the disc. Now draw another 90 degrees to that one so you have a big +.
Step 3: Punch Some Holes Draw More Guidelines and Thread Some String
Using the hole punch, make a single hole on one of the lines, a little way in from the edge of the disc.
Do the same at the other end of the line.
Now flip your disc over and draw another +. It needs to be aligned with the one on the other side. Use the holes to help you position the first line, find it's midpoint and then draw another line at 90 degrees.
Thread a length of string through each hole and tie it on securely.
Alternatively you can use rubber bands or elastic. I did this because you don't have to continually twist the disc, you can just wind it up and let it go.
Step 4: Get Arty
This is the most difficult step. Not because it requires any great artistic talent, but because you have to line up your drawing so that they merge properly through persistence of vision.
The thing to remember is that once you've drawn on one side you must flip your disc over top to bottom. In other words, turn it over as it would turn if you were spinning it with the strings. This ensures that your images will be the correct way up.
The guidelines are there to help you position your artwork so that the two sides merge properly.
My designs of two figures embracing and a loved up face seemed like good ones for Valentine's Day, but you can do anything where one thing merges into another. Be creative and romantic!
As an extra final step I laminated one of my thaumatropes to make it a bit more rugged.
That's it! Have fun and be lovely.