Chemicals like N-methyl pyrrolidone and toluene are renowned for their ability to dissolve paint. But the properties that make them effective solvents also make them harmful to people and the environment.

NMP and toluene are listed under California’s Proposition 65 as chemicals known to cause developmental harm. Toluene is also listed as a hazardous air pollutant under the federal Clean Air Act.

The Department has spent the past three years trying new solutions with everything from baking soda to dry ice, and Nuru said they’re focused on eliminating as many types of harmful chemical solvents as possible.

Dry ice is the solid form of carbon dioxide. Small pellets of ice are pressure-blasted onto surfaces where they freeze the graffiti, causing it to expand and explode off the surface of a bus or building.

After hitting a structure the dry ice turns into a gas and returns into the atmosphere as carbon dioxide, leaving no residue behind. The amount of CO2 is negligible, according to Ben Shepard of Cold Jet, which manufactures a high pressure blaster for dry ice.

San Francisco will also be testing sand and a soy-oil product.

The soy contains methyl ester, a compound in vegetable oils that can remove certain types of paint. It’s mixed with rubbing alcohol and can be wiped onto surfaces without a heavy duty sand blaster.

The sand is made from old beer bottles and other recycled glass that is ground into a fine powder that is pressure-blasted onto graffiti to scrape it away.

Peanut oil was an early contender since it removes spray paint from stop signs the way peanut butter removes gum from hair. But the prevalence of nut allergies among many people squashed that solution.

“They all kind of sound like home remedies, I mean who would have thought peanut butter?” Blumenfeld said. “But cities across the nation are feeling a budget squeeze, so many of these things like soy or the recycled glass are actually cheaper than the toxic alternative.”

For all their novelty, the natural materials can’t dissolve the graffiti itself. The tiny bits of paint that are blasted or wiped off may still contain harmful chemicals.

“We are not a magic wand,” Shepard said. “If we were, you would just point the nozzle and what you cleaned would disappear, sadly, we’re not there just yet.”