[thedoc (OP)]

Paul Anderson  asked the Naked Scientists:
   
Unfortunately there are cretins in NZ who graffiti.

I was listening to a podcast recently about several layers of fingerprints now being able to be lifted from objects.

I have also heard about research into "invisibility"

I also have a work mate being zapped next week for tumours in the brain.

I do not know much about colour other than different colours have different frequencies. Actually that has just given me another idea. In computer graphics now you can doctor photos by getting surrounding colour to cover over parts of the photo.  Would it be possible for a person to have some sort of electronic gun which works by sending out a pulse at a wall and the returning signal is analysed to give the colour of that part of wall. Then some sort of energised pulse is sent out which strikes wall surface atoms which are not part of the main colour of the wall and gets them into a state where they either reflect the same colour as the rest of the wall, or become translucent, so one can see the original colour of the wall underneath the graffiti, or am I just getting carried away in some sort of science-fiction dreaming?

If I am dreaming, what about astronomers who analyse what chemicals make up the planets?

Regards

Paul
What do you think?

[Tinker-Bell]

"Everything should be made as simple as possible but not ANY SIMPLER." - Albert Einstein (requoting Occam's Razor)

"Everything should be made as simple as possible but not BEYOND NECESSITY." - William of Ockham (Author: Occam's Razor; requoted by Toad)

The SIMPLEST answer to the Graffiti problem is ...

IGNORE IT!

"That which matters should NEVER be at the mercy of that which does not." - Goethe

"Take 'n0thing' serious and wash-down everything-else with Vodka." - Dick Van Dyke (aka: Martini Proverb)

"To know everything is to know n0thing." - Socrates

Ribbit 

[RD]

Paul Anderson  asked the Naked Scientists:
... what about astronomers who analyse what chemicals make up the planets?

Absorbed light, rather than reflected light, gives-away the chemical signature of planet's atmosphere ... 

https://wikipedia.org/wiki/Absorption_spectroscopy

[Colin2B]

Many pigments and dyes are affected by light, particularly UV, which causes them to fade. To fade the colours quickly would require quite a lot very bright (and possibly generating a lot of heat as well) light, but in theory could be done.

[vhfpmr]

There were some council workers removing graffiti on the news a few days ago, they didn't seem to need anything more sophisticated than high pressure water jets.

[evan_au]

Could a device select atoms by colour, then act on them?

There have been attempts to separate isotopes by tuning lasers to the precise colour of different isotopes.
See: https://en.wikipedia.org/wiki/Atomic_vapor_laser_isotope_separation

Diamonds are already separated from crushed rock by shining X-Rays on them, which causes them to glow. This activates a mechanism to divert the diamonds for separation from the dirt.

Would it be possible for a person to have some sort of electronic gun which works by sending out a pulse at a wall and the returning signal is analysed to give the colour of that part of wall.

The Mars rover "Curiosity" has a laser beam that evaporates small samples from a surface (eg rocks), and then uses the spectrum of light to determine the chemical composition of the surface.
See: https://en.wikipedia.org/wiki/Curiosity_(rover)#Chemistry_and_Camera_complex_.28ChemCam.29

Unfortunately there are cretins in NZ who graffiti.

There are also some great computer graphics production companies in NZ (eg Weta Studios, who did the graphics for the Lord of the Rings).
If only we could get the two groups to work productively together!