Laying down circuits using a mainstay of industrial chemistry. By Sarah Hansen
When you see a thin layer of metal – on anything from chrome car parts to drill bits to jewellery – electroplating has probably been at work. The process is simple: send current through a metallic salt solution to coat a conductive surface with metal ions. In this project, we’re coating graphite (in the form of a pencil drawing) with copper, the material in electric wiring. This turns the image into a circuit that can supply an LED with power. A new way to wire your house? No. Cool? Definitely.
1. In a clear bowl, combine 3 tablespoons of copper sulphate with 1 cup of white vinegar. Stir with a straw. When the vinegar turns blue, the copper is dissolved.
2. Use fine sandpaper to roughen a piece of transparency film.
3. Draw an image on the scratched film with an HB pencil. Your picture needs to consist of a single, thick line and extend to the edge of the film.
4. Clamp a red alligator clip to the positive terminal of a 9-volt battery. Clamp the other red clip to the mechanical pencil graphite.
5. Clamp a black alligator clip to the negative terminal of the battery. Clamp the other black clip to the edge of your drawing.
6. Without letting the alligator clip touch the liquid, submerge the film in the bowl. Tape the clip to the edge of the bowl.
7. Submerge the pencil lead in the solution. Tape its alligator clip to the bowl. The dissolved copper will plate on to your drawing. (You’ll see bubbles form on the lead.)
8. When the drawing is completely covered in copper, disconnect the clips from the battery and dry the drawing with a paper towel.
9. Test the copper with two separate plated drawings. Connect one drawing to the battery’s positive terminal with an alligator clip, and the other one to the negative terminal with a second clip. Touch one leg of the LED to each drawing; let there be light!
Sarah Hansen teaches chemistry at Columbia University and researches chemistry education at Columbia’s Teachers College.