The word “graffiti” usually conjures images of people with spray cans illegally making murals or jotting down tags using colorful paints. A lot artistic interventions use other tools and materials, though, subverting expectations and working in (literal and legal) gray areas to create works without leaving a conventional trace. Consider, for instance, the massive deep sea monsters, jungle predators and swamp creatures of Russian illustrator Nikita Golubev that lurk in the grimy shadows on the sides and backs of trucks.

Along similar lines, this series of skulls by artist Orion was made by scrubbing car exhaust from an active tunnel. For those looking to deter street art and artists, subtractive interventions like these can be tricky to pin down. After all, Golubev and Orion are simply cleaning vehicles or public surfaces, albeit very selectively. In many cases, the end result is actually further cleaning — art like this often pushes municipalities to send out teams that then wash off entire areas to make them look consistent again.

This artistic approach draws different reactions depending on the scale and situation. Take snow calligraphy, for instance — few people seem to mind a nice message traced into the hood of their car. Artist Faust notes that virtually “everyone has an affinity for writing in the snow as a child,” so perhaps it’s also something people feel they can relate to on a more experiential level.

Reverse graffiti not only provokes different response—it also spans a variety of materials and methods and can work with greenery as well as it does with snow or grime. Some moss artists work additively, creating mixtures to apply to surfaces and thus encouraging moss to follow particular grown patterns to produce an specific result. Others, however, actively remove moss to create desired words, patterns and illustrations.

Stefaan de Croock falls into the latter category, using power-washing tools to create cityscapes and other whimsical scenes on surfaces previously covered in layers of moss. As with a lot of reverse graffiti projects, his pieces are generally temporary — the moss simply grows back in to fill the voids over time.

SpY’s work in Besancon, France, combines elements of reverse graffiti and tree sculpting. Turning topiary approaches into a mural-making technique, he shaped vines into a circular work of wall art using an elevated work platform, trimming his way toward a perfect circle.

Light art and projection bombing are even more temporary and generally even less invasive than reverse graffiti. Lighting machines aimed at buildings to create patterns or spell out messages can be targeted and disabled if they persist, but ephemeral light painting like the above work by Lichtfaktor are deployed quickly using glowsticks or other portable devices and have to be captured on camera to work, making them brilliantly elusive.

Meanwhile, if light art is about brief visibility, then hydrophobic spray art is about lasting invisibility. Both are made to be seen and not seen in particular ways, but the latter has a key ingredient that determines when a design or artwork is visible: wetness.

When the hydrophobic NeverWet spray came out, it promised to waterproof everything, but some users found they had mixed results in applying it to things like clothing and touchscreens – it discolored shoes and left a sticky film on devices. Then someone thought to create a stencil and tag sidewalks with the stuff and a new type of visible-when-wet graffiti was born. One can, of course, free-spray with it as well, but stencils help make the outcome more controlled and predictable.

The same basic artistic idea has been applied in other contexts by designers, too — selective hydrophobia can be incorporated into brick pavers or concrete sidewalks, for instance, to create patterns that change with the weather. Clever urbanists might consider ways to integrate useful messages or wayfinding elements into such projects, like arrows pointing to nearest sources of shelter in a storm. Similarly, messages that appear on surfaces that change color with temperature could be used to guide people on particularly hot or cold days.

Practical designs aside, artists continue to experiment outside of traditional material palettes with works that raise questions about visibility and invisibility. There is fun to be found at the intersections of these ideas, embodied in projects like this one by 3D artist Milane Ramsi, who combined different approaches into a single installation — a concrete pillar appears to vanish while simultaneously revealing three-dimensional lettering more reminiscent of conventional graffiti.

Additive or subtractive, vandalism has its grey areas, but what about the seemingly more straightforward removal of graffiti? Here again there are shades of gray. Some artists, like Mathieu Tremblin, paint a surface clean then write over graffiti with their own work — in his case: humorously replacing loose tags with digital-style tag clouds. That, clearly, is of a kind with what was underneath; in places where tagging is illegal, replacement tags are too.

Then there is the saga of the infamous Banksy and the so-called Gray Ghost, an anti-street artist who leaves signature splotches of gray in the wake of his graffiti removals. Some argue the Ghost’s work vandalizes art — others say it is itself art. Legally, like Banksy’s illegal murals, both artists work in a similar space, though in Banksy’s case building owners often go to great lengths to preserve his art, in part for its monetary value.

Exceptions aside, municipal laws are usually clear on painted public art and the goal is generally total graffiti erasure, though it doesn’t always work out that way. This kind of official cleanup usually draws binary responses, viewed by some as a welcome fix and by others as an act of defacement. One award-winning film, however, argues for a third point of view: graffiti removal as the ultimate next step in the progression of modern art. Despite its semi-satirical intent, The Subconscious Art of Graffiti Removal raises provocative questions about what constitutes street artwork in the gray areas of additive and subtractive graffiti.

Artist Jenny Holzer is known for making public statements that can’t be ignored, and her latest project brings stark messages about gun violence to the facades of New York City’s Rockefeller Center. For “VIGIL,” a three-night installation that took place October 10-12, Holzer projected poems by teenagers impacted by school shootings, texts from the compilation “Bullets into Bells: Poets & Citizens Respond to Gun Violence” and stories from “Moments That Survive,” a collection by Everytown for Gun Safety.

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Presented in collaboration with the public arts organization Creative Time, “VIGIL” leaves onlookers no choice but to absorb and grapple with these messages and testimonies. The project aims to center the voices of those directly affected by gun violence, shifting away from using faceless statistics to emphasize the human toll.

“Projected onto one of the most iconic landmarks in New York City, VIGIL speaks to the massive impact gun violence has not only on individuals, but the very fabric of communities and cities,” reads Creative Time’s curatorial statement on the project. “The text encroaches on the facades and windows of these buildings, surrounding the viewer and enveloping the city in messages of light. Through the project, the city itself is transformed.”

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“The scrolling words of Holzer’s projections demand that the audience reads them. This strategy denies passive engagement, as viewers internalize these messages by hearing the text in their own voice. It is not possible to let these words just wash over. Since 1991, Holzer has used this technique to address such issues as domestic violence, war, and the corruption of power. Throughout her career, she has aimed to bring to light that which is hidden. In her ongoing project It Is Guns, trucks equipped with LED screens share pointed texts by the artist similarly addressing gun violence. Holzer expands upon these issues in VIGIL, magnifying her messages from the street to the cityscape.”

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See more photos of the installation at Gothamist.

Photos by Lauren Camarata

Three years after decorating Paris with smartly-dressed animals, street artist Julien Nonnon is back with a project that temporarily adorns the streets of Hong Kong with his own modern version of the Chinese Zodiac. Founding member of creative studio Le3, Nonnon walks the streets of cities around the world with a mobile projector for a series he calls ‘Street Mapping.’ Ordinary building facades and other urban surfaces light up with imagery, captivating passersby for a few brief moments before disappearing.

The traditional Chinese zodiac features twelve animals: ox, tiber, rabbit, dragon, snake, horse, goat, monkey, rooster, dog, pig and rat. For this ‘Urban Safari’ series, Nonnon transformed each sign into an anthropomorphized character in contemporary clothing, each animal interpreted in various ways.

Many of the animals are holding cell phones or shopping bags, sipping coffee or gazing contemplatively out onto the city below. Some stand as high as six or seven stories, looking like phantoms wavering against the darkened facades of tall buildings. Nonnon doesn’t reveal his methods, only saying he developed his own tools to bring his work to life.

Over a dozen installations are bringing Japan’s 5,000,0000-square-foot Mifuneyama Rakuen to life, combining nature with cultural traditions and modern technology in dazzling and moving ways.

Designed by TeamLab, this exhibition incorporates a sweeping landscape of lakes, mountains and forests as well as ancient structures, some predating the park (which itself is nearly 200 years old).

Their driving idea: create new immersive interactions with nature without doing any damage, using an array of lighting techniques to facilitate a unique nighttime experience. In some places, abstract lighting patterns contrast with or highlight natural elements, like koi fish swimming in a lake — in other instances, projections of scanned nature illustrate the cycle of seasons in underground caves.

“Winding promenades, a picturesque pond and an ancient villa-turned-tea house blend seamlessly with the natural surroundings, blurring the borders between wild and manmade,” reports DesignBoom. “High above, the monumental mifuneyama mountain watches over an active and lush ecosystem of sacred trees, ancient stones, hidden caves, and a diverse community of flora and fauna. It is a peaceful and poetic place that induces a deep sense of contemplation and calm. Serenity lives here.”

Visitors can journey through this hybrid wonderland moving from one exhibition to the next in sequence, or simply get lost in the trails that open each evening as the sun goes down. The project, titled “A Forest Where Gods Live,” is open through this fall.

Exposed to the elements, hand-painted signs on building exteriors chip, crack and fade over time, but one artist is shining a spotlight on these historic illustrations, restoring them through animated and layered projections.

Craig Winslow is meticulous about his work on “Light Capsules,” digging through archived newspapers, magazines and photographs to find ads showing what these signs and their typogrophies originally looked like (in some cases over 100 years ago). The result of one such search recently helped him project over an ad in Winnipeg, Canada for Porter & Co., crockery, china, glassware, lamps, silverware, cutlery, which then switched to another projection for The Home of Milady Chocolates on the same spot.

And it isn’t just about recreation, but also spectacle and preservation. People passing by, used to ignoring faded signs, suddenly stop, look up and start thinking about them and the histories they represent as well as their historic value to a city.

In the last few years, Winslow has brought his projections to cities around the world including Detroit, London and Los Angeles. A lot of the advertisements he projects over provide insights into what was popular in the early 1900s when hand-painted signs were common.

His projections are often layered, cycling through to highlight different stages of ads (or overlapping ones) that have evolved and changed over the decades. Importing digital images, Winslow uses a suite of editing tools to fill in the gaps and create animations.

And while some argue for restoring them outright (using paint), that can be problematic — critics say repainting ruins the authenticity, plus new paints tend to be more vibrant and would be unlikely to represent the original. In a way, Winslow has found a middle ground — his method lets people get a sense of what they looked like without putting the originals at risk.

More from the artist’s website: “There’s an extra element of excitement in signs that are incredibly worn or have multiple layers—The best ghostsigns candidates to become Light Capsules have multiple layers, called palimpsests, providing a compelling canvas which digital recreations can bring a focus to specific layer in time. Projection is ephemeral, non-damaging, and non-invasive, providing a strong preservation solution that traditional mediums can’t provide. Using light as a medium, we can visually explore the stories of every layer, seeing how a building changed throughout the years.”