Practical magic—the moiré effect

I love the moiré effect. It’s so magical and surprising the way it springs from very simple, static elements. The patterns that are created can be very beautiful and dynamic. It really does feel like you get far more out than you put in.

I’m working on a kit for kids to allow them to explore the moiré effect. It consists of simple graphic patterns printed on to white card and repeated on clear acetate. When you place the acetate directly over the corresponding card the identical designs line up, then by shifting the acetate you will instantly create moiré effects.

The moiré effect varies a great deal depending on the original graphic pattern being used—its density, complexity, boldness/lightness and the arrangement of its elements. The effect also depends on how you move the acetate sheet.

With concentric circles, if you move the sheet of acetate in a circle around the centre of the card below you will create a very strong illusion of rotating bands, radiating from the centre.

With lines graphic lines radiating from the centre the moiré effect appears rich, complex and full of movement.

Parallel vertical lines create moving horizontal bands as you rotate the acetate sheet. The more you rotate the acetate the more bands appear, within an arc of about 30º. Hold the acetate at an angle and move it to the left or right and the horizontal bands will appear to move upwards and downwards. When the lines are very close to parallel the bands are thicker and any minute shift in the acetate creates a lot of apparent movement.

A random spread of dots requires very little movement of the acetate to produce a striking but subtle moiré effect. One that dissolves instantly at the point where the brain no longer sees a relationship between the dots on the paper and those repeated on the acetate. Rotate the acetate and the effect created is a kind of radial blur that looks like long exposure photographs of stars processing. If you then move the sheet up or down, the centre point shifts.

Here are a few more that built on the effects already described:

Below you can see what my son and his friend made of this set of patterns. My aim now is to make a short run of pattern packs to test whether people would be interested in them.

In the meantime here a couple of things I saw that got me excited about moiré in the first place.