You may question what possible relevance this information has for you.
I would reply that I found myself agreeing to make not just one, but two scratch-and-sniff maps of New York City almost entirely by accident earlier this year. And even if you are more sensible than I am, and would never agree to such ill-informed adventures, it turns out that the magic of scratch-and-sniff map-making opens an entirely new perspective on the world -- an unexpected and invisible cartography of emotion, confusion and memory.
The first step, of course, is to decide what smells you are mapping. (The rest of the how-to comes a bit further down the page). Perhaps the earliest attempt to make an urban smell map dates back to Paris in the 1790s, when new ideas about both political equality and hygiene combined to send physician Jean-Noël Hallé on a six-mile odor-recording expedition along the banks of the Seine. His map-making technology consisted of nothing more than a notebook and pencil -- and, of course, his nose.
Today, artist Sissel Tolaas is the world's pre-eminent olfactory cartographer. She is midway through a survey of Kansas City, having already smell-mapped Paris, Vienna and Mexico City, with Nuuk and Calcutta next on her list. Although Tolaas still relies heavily on her nose, which she has spent years training, she also has a couple of important tools at her disposal, as she described her urban smell mapping process to me:
I try to go back to sites a couple of times to identify which smells remain over time and which change. If I have the time, I go back in different seasons and in different weather, so I can see which smells are important, underlying smells and how they change in different conditions. And I focus on finding the source for smells. If the source is definable and tangible, I can grab a sample and do a chemical analysis using a GCMS [a gas chromatograph/mass spectrometer] in my lab. If the source is not something that's portable, and if the budget allows, I will bring headspace technology into the field.
"Headspace" refers to a prohibitively expensive and utterly fascinating technology invented in the 1980s by Dr. Braja Mookherjee, a scientist at IFF, one of the world's largest fragrance and flavor companies. Mookherjee was obsessed with capturing the exact odor you experience when you put your nose up to, say, a living jasmine flower, rather than relying on an extract, or "absolute," as it's called in the perfumery business. In a paper (pdf) published in 1990 -- the same year IFF trademarked Mookherjee's discovery as "IFF Living Flower Technology" -- Mookherjee described his dissatisfaction with natural oils and extracts:
Before the extraction process, the fruits, flowers, and other plant parts must, of course, be picked. Very few people are aware of the fact that most fruits and flowers when picked soon exhibit a modified aroma from that of the living entity. This aroma continues to change with the process of decay. Hence, the oil obtained from the picked plant part does not replicate the aroma of the living material.
Sadly, Dr. Mookherjee passed away a few years ago, but Helen Murphy, IFF's Director of New Fragrance Development, explained how his process works to capture the odor your nose actually smells:
The idea is to capture, analyze, and then create the smell of nature. We use a special apparatus that captures the volatile components from the air surrounding the flower, fruit or plant. This is then analyzed in our R&D labs using a GCMS analytical machine that gives a fingerprint of the ingredients found in the flower. It is then possible to recreate this smell by putting together the different ingredients that were found in the analysis.
In order to create new raw ingredients for their perfumers and flavorists, Murphy told me that IFF has performed headspace analysis on an entire, specially planted botanical garden (above) full of fruit, flowers, herbs, and seeds. If her team finds an interesting or new smell, they can simply request a headspace analysis. "We have a huge library of these Livings," she said. "You don't have to limit it to flowers, obviously. We've used it to do things like the smell of a stone, the smell of mothers' milk, and even the smell of the skin of a virgin."
For IFF's perfumers, the smell of a street corner in London is just another ingredient, to be combined and blended with other notes to make it more wearable, complex or beautiful. For Tolaas, that same smell is information that can be used to both navigate and understand the city. Rather than improvise upon odiferous reality, she creates a map built of smells, exactly as she found them.
But aspiring smell-mappers need not only document reality. Just like their non-odorous counterparts, smell maps can chart a layer of personal experience, history or social trends atop spatial reality. My maps, for example, which are now on display as part of the "You Are Here" exhibition at the Pratt Manhattan Gallery, sit side-by-side to compare New Yorkers' majority and individual smell preferences.
In other words, my scratch-and-sniff maps show how New Yorkers' smell, rather than what. To make them, I extrapolated data from the as-yet-unpublished results of an extensive study that tested the responses of four hundred New Yorkers to sixty-six different smells over a two-year period from March 2005. The experiment was conducted by Andreas Keller and Leslie B. Vosshall at the Laboratory of Neurogenetics and Behavior, The Rockefeller University.
"Our main goal was to try to find the difference between different variants in the DNA and different ways that people rank the smells on a seven-point scale from extremely unpleasant to extremely pleasant," Keller said. "We collected our subjects' demographic information just to control for those types of influences."
Nonetheless, that demographic information revealed some fascinating and significant differences in smell perception between men and women, young and old, and different ethnicities. For my map, I chose twelve of Vosshall and Keller's most interesting test smells, from complex natural extracts such as nutmeg and vanilla to single-note synthetic molecules such as octyl acetate, which is the basis for many artificial orange flavors as well as a key ingredient in Chanel No.5.
Sourcing those chemicals was tough enough -- some, such as galaxolide, an artificial musk, were so jaw-droppingly expensive that I was lucky to secure a donation, while others only came in five-gallon barrels (I needed roughly a pound to make a thousand stickers), and all had to be shipped as hazardous material. Most came from chemical supplier Sigma Aldrich and IFF itself.
But I was lucky, because at least the smells I was working with were popular enough to be commercially available. Sissel Tolaas told me that she frequently struggles to find the "bad-smelling" molecules she needs to recreate reality.
Still, with the odorant chemicals in hand, my next challenge was to work out how to turn them into scratch-and-sniff stickers. I turned to a Chattanooga-based company, Arcade Marketing, whose business is to provide sampling solutions to fragrance, cosmetics and food companies. If you've ever peeled back a perfume ad in a glossy magazine, chances are it was made by Arcade.
According to Anne Spratt, Arcade's Director of Fragrance Lab Services, to make the stickers for my map, she used a proprietary technique called MicroFragrance Scratch 'n' Sniff technology to microencapsulate the chemicals I sent them, and then apply the resulting slurry to clear stickers.
"We put your materials in our test lab reactor where they were mixed at high speed to form droplets in an emulsion," Spratt told me. "The speed at which we mix determines the size of the droplets and we're making very small droplets that are less than twenty microns in size. They are not visible to the naked eye."
Arcade then adds proprietary ingredients (including some kind of water-soluble polymer), which allow a "wall" material to form around the droplets, in order to create microcapsules. Under carefully controlled conditions of time, temperature and pH, this wall will harden, leaving the microcapsules of fragrance suspended in a sort of slurry. At this point, you're nearly there, as Anne explained:
The reaction begins on day one. If the encapsulation goes perfectly the first time, a process involving heat conditioning of the capsule walls then runs overnight. On day two, we formulate the slurry, adding some binder to help it adhere to the surface on which we are printing. Finally, we print the adhesive-backed sample labels -- your "stickers" -- using a flexographic press.
The basic science behind the process was developed by chemists at the National Cash Register company in the 1950s, who were looking for a better way to make the customer copy of a receipt. Barrett K. Green and Lowell Schleicher were awarded a patent for their "Manifold Record Material," or carbonless copy paper, in 1956.
A secretary, they explained, would simply put two sheets of paper in their machine -- the top one coated with "a profusion of microscopic color-reactant-containing, pressure-rupturable capsules" and the bottom one sensitized with an "acid clay-like material," and begin to type. Each keystroke would rupture only the microcapsules it hit, releasing colorless ink in a letter shape onto the bottom sheet, whose pH made the invisible droplets visible -- thus creating a perfect copy without the need for carbon paper. With some reformulation (early versions exposed office workers to high levels of Bisphenol A), Green and Schleicher's carbonless copy paper is still available today, providing non-electronic copies of prescription forms, parking tickets and more.
Rival company 3M quickly patented their own version of microcapsule-filled copy paper using a different wall material, and it was their marketing team that realized that the capsules could just as easily hold scented oil as ink. The late 1970s and early 1980s saw an explosion of scratch-and-sniff stickers, games, cards, books and even movies -- cinema audiences for John Waters' Polyester were given Odorama cards impregnated with smells of pizza, glue and feces.
Today, microencapsulation technology is widely used to delay ingredient release in stain removers, pharmaceuticals and even packaged baking mixes, while scratch-and-sniff has retreated from popular culture to become the preserve of fragrance, cosmetics and household goods' marketing materials. Nonetheless, Marine Ravera, Marketing Coordinator at Arcade, told me that they are "increasingly getting into more exploratory kind of work, where the goal is not selling things but raising people's awareness and interest in smell." Among their most exciting recent projects, for example, was using a new "peel and reveal" technology to create a souvenir program for perfumer Christophe Laudamiel's 2009 "Scent Opera" at the Guggenheim.
Meanwhile, artist Sissel Tolaas has experimented in her lab to formulate a slurry that can be applied to a wall like paint (used to embed the smell of money into the walls of a Swiss bank's wealth management offices) as well as a version that can be printed on T-shirts, "so you can wear your own sweat around, but it's only released by touch."
Scratch-and-sniff microencapuslation is also amazingly durable. Spratt and Tolaas agree that you can scratch each sticker hundreds -- even thousands -- of times before all the tiny capsules are broken and their smell released.
It is precisely this aspect of scratch-and-sniff -- the fact that the invisible smell information can only be revealed by touch -- that makes it such a perfect technology for cartographic investigation. At my gallery opening, for example, I saw long-time New Yorkers and visitors alike became modern-day explorers, scouting this new world with their fingers and noses pressed up against the wall.
A scratch-and-sniff map, in other words, forces us to relearn ourselves and our environment using only touch and smell. As Sissel Tolaas puts it, perfectly:
People don't know how to communicate what they perceive through the nose, and so the city becomes a playground again. This is a lot of fun, but it's also how we can acquire new knowledge -- through this playful exploration.
[Note: Arcade Marketing generously made the stickers for my scratch-and-sniff map at no cost, while International Flavors and Fragrances (IFF) kindly donated two of the smells (including the galaxolide) and the Laboratory of Neurogenetics and Behavior at The Rockefeller University shared their data and helped me dilute my smells. My installation, Scratch 'N Sniff NYC, is on display through November 6 at the Pratt Manhattan Gallery, 144 West 14th Street, 2nd floor, New York, NY 10011; gallery hours are Tuesday-Saturday 11:00 a.m.-6:00 p.m. and entry is free.]
Images: 1. Instructions and sampling station for personal smell preferences, from Scratch 'N Sniff NYC by Nicola Twilley, photo by Andreas Keller of the Vosshall Lab; 2. Sissel Tolaas on a smell walk; 3. IFF's headspace technology in action, photo courtesy IFF; 4. Aroma Emissions Analysis System drawing from Patent 5355718, Braja D. Mookherjee et al.; 5. Comparison of GCMS results for a living and picked peach from "The chemistry of flowers, fruits and spices: live vs. dead a new dimension in fragrance research," a 1990 paper by Braja D. Mookherjee, Robert. W. Trenkle, and Richard A. Wilson; 7. IFF Botanical Gardens, New Jersey, photo courtesy IFF; 8. Two scratch-and-sniff maps of NYC, showing majority smell preference and emerging, crowd-sourced personal smell preference side-by-side, from Scratch 'N Sniff NYC by Nicola Twilley, photo by Andreas Keller of the Vosshall Lab; 9. Personal smell preference map, showing wildly varying smell descriptors, from Scratch 'N Sniff NYC by Nicola Twilley, photo by Andreas Keller of the Vosshall Lab; 10. Drawing from Patent 2730456, "Manifold Record Material, Green et al.; 11. Collectible scratch-and-sniff stickers from the 1980s, via; 12 Odorama card for John Waters' Polyester, via; 13. Fear 9 by Sissel Tolaas, in which the gallery wall contains microcapsules of the recreated smell of sweat collected from the armpits of nine phobic men exposed to their worst fear; 14. Scientist Leslie B. Vosshall and her daughter Ophelia scratch and sniff New York City at the opening of the "You Are Here" exhibition, photo by Andreas Keller of the Vosshall Lab.