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.

Waterproof and windproof seem like small bonus features next to the dazzling look of this jacket design, the shell of which is covered in microscopic spheres that mimic the adaptive camouflage of squids.

Developed by Vollebak, this high-tech creation used lasers to embed these tiny balls into resin along the triple-layered surface of the garment, creating a slick metallic oil-like effect by day and then a dazzling spectrum of reflective wonder at night.

“The Black Squid Jacket focuses on replicating the elements of squid skin that make it hyper-visible,” explains the designer. Whereas “a squid uses microscopic plate-like structures on the surface of its skin to change color, our jacket uses disruptively-structured microscopic glass spheres.’

“When light hits the jacket, it travels through the curved surface of these black glass spheres and strikes the back of them, before being reflected back at the original light source and scattered away from it simultaneously, so that the fabric looks like it’s emitting light.”

Within two years, the city of Chengdu aims to swap out its ground-based street lighting with the soft glow of an artificial moon, casting light across 50 square miles of the urban landscape.

Wu Chunfeng, chairman of Chengdu Aerospace Science and Technology Microelectronics System Research Institute, announced the news at a national mass innovation and entrepreneurship event earlier this month.

Reflective panels on board the machine will pick up and redirect the sun’s rays. The satellite will actually glow multiple times brighter than the moon itself, creating a dusk-like atmosphere on demand. The precise illumination can be varied in different sections of the city as well.

The project may sound like a moonshot but it’s not without precedent: Soviets tested similar light-reflecting satellites decades ago, aimed to illuminate darker northern regions, and on the ground: cities in valleys have also been known to use giant reflectors perched on adjacent mountainsides.

Working with Formula 1 race car manufacturers and employing aerospace materials, a Swiss firm has developed what they claim is the world’s lightest wheelchair, with a frame weighing in at just 3.3 pounds.

Significantly lighter and stronger than typical high-performance carbon variants, Kueschall employed graphene (which can be hundreds of times stronger than steel and significantly tougher than diamond) to lighten the load while making the machine more durable.

“A single layer of carbon atoms, tightly bound in a hexagonal lattice” was at the heart of the engineering strategy. Why bother to make even lighter models? The firm points out that over half of wheelchair users end up with upper body damage over the years. Aside from the materials, “in order to ease these chances the wheels have been positioned in closer proximity to the user which helps to increase propelling efficiency.”

Industrial designer and project leader for the company, Andre Fangueiro, worked “to perfect the driving performance of the Superstar. The wheelchair features an X-shape geometry with road dampening properties that provides an increase in performance and agility by responding rapidly to every movement. It also features a bespoke backrest with the possibility for a tool less adjustment, and a tailor made seat with an integrated seat cushion to also help optimize propelling performance.”

Flowing out like the rings from the center of a tree, the veneers on this chest of drawers were carefully selected, perfected and oiled to create a remarkable effect.

The lightening of the wood as it pushes outward creates a compelling organic variant, and reinforces the impression that the whole piece was cut from a single tree. In reality, it was meticulously created using a combination of fumed oak, brown oak, oak, olive ash and ash.

Designer Edward Johnson says the inspiration was partly aesthetic, but also a nod to longevity — rings signify the passing of years, and his pieces are crafted to be durable as well. Small details, like a curved base and finger slots, play on the contrast of circular and rectilinear shapes.

Meanwhile, the “radiant desk takes on a sculptural asymmetrical design and is constructed from fumed and brown oak … veneers flow seamlessly from a semi-circular core that radiates out and down each side of the feature aerofoil shaped legs.”

The process can be painstaking. “Hundreds of thin strips of wood are cut in the workshop and joined back together using contrasting tones, resulting in sweeping lines and curves that envelop the furniture, bringing a soft, organic surface to the angular forms.”