How Does Scratch and Sniff Work?

Scratch and sniff was born of the noble endeavor of making copies. In the dark ages before word processors, inkjet printers, and the Xerox machine, copies of documents were made by placing carbon paper between the sheet you were typing on and the sheet that would become the copy. In the early 1960s, an organic chemist at 3M named Gale Matson developed a way to make ink copies without carbon paper, using a process called microencapsulation.

The Matson process uses two sheets of paper "“ one for the original document and one for the copy "“ on top of one another. The top sheet of paper is coated with microcapsules of colorless ink. When someone writes or types on the paper, the capsules break and release their ink, which mixes with a developer chemical on the second sheet to create a copy.

Not wanting Matson's technology to be a one trick pony, 3M began to search for alternate uses for micro-encapsulation and found that it could be applied to scented oils as well as ink. Scratch 'N Sniff debuted in 1965 and is found in various forms, from stickers to pull-apart perfume sample strips and beyond.

How It Works

1. Scented oil is mixed with a solution of water and water-soluble (capable of being dissolved in water) polymer (3M uses polyoxymethylene urea) in a large vat called a reactor.

2. The mixture is blended at a high speed by a rotary blade. As the oil and polymer solution mix, the oil breaks into very small droplets. After about 12 hours of blending, the droplets are about 20 to 30 microns in size, invisible to the naked eye.

3. When the droplets are the right size, the blending is stopped and a chemical catalyst is added. The catalyst causes the molecular weight of the polymer to increase and become water insoluble. The polymer precipitates out of the water and forms a shell around, or encapsulates, each individual droplet of oil.

4. The reactor is stopped, and the microcapsules are collected and washed to remove any unreacted or unencapsulated materials.

5. The capsules are placed in a tank and mixed with a water base and an adhesive, forming a thick slurry.

6. The slurry is ready to be applied to paper, and there are four basic methods for doing this: silk-screening, web offset printing, flexo-graphic printing (this is what is used for scratch and sniff stickers) and extrusion (a fairly complex printing method used for making perfume and cologne sample strips).

Smelling the finished product is just like smelling anything else. When we scratch the surface of the paper, the microcapsules break and the scented oil travels to our nasal cavity, where the molecules are detected by the olfactory sensory neurons in the olfactory epithelium. A signal is sent to the brain, which translates it, and then we say, "Oooh, banana!"

Click & Sniff

We've come a long way since the birth of Scratch 'N Sniff, and now we don't need micro-encapsulation to smell exotic scents whenever we want. Heck, we don't even need to scratch. Here are some more recent developments in digital scent technology.

DigiScents Inc. in Oakland, California, created the iSmell scent synthesizer. You insert a scent cartridge into the iSmell, which is connected to a computer or video game console, and it releases the scent in short bursts at appropriate times, i.e. when you're playing a first person shooter and get into a firefight, you'll actually get whiffs of gunpowder as you fire rounds. Before you get too excited, PC World named the iSmell one of the 25 Worst Tech Products of All-Time.
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ScenTeck Technologies' Scratch-N-Sniff Pro software and System Scent Card replace the standard vibrating sound waves coming from computer speakers with unique vibrating tones that the brain recognizes not as a sound, but a scent.
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Unleashed, an album by Savannah, Georgia-based musician Zan, is the world's first scent-enabled CD. A gadget called a Scent-Dome plugged into your computer reads code embedded in the CD and releases different scents as the songs play.