In an age before computers became our master form of communicating , invisible ink was a favorite style to pass information without draw in unwanted attention . It may have always been more common in detective stories than real life sentence , but it was easy enough to make at rest home . The idea may be less important in popular culture as information technology develop , but fluorescent ink that can only be show under ultraviolet light are in increase demand for text file security . exist ones just do n’t work all that well .
Traditionalhome - made invisible inksmay have been big for a hired hand - scrawled bill telling hoi polloi where to search , or who to appear out for , but print foresighted written document is something else . For all the role computers play , “ Paper still plays a predominant role in selective information storage , ” a raw subject in the journalMatternotes .
By coating composition with a manganese complex researcher at Nanjing University have turned it into a sort of effaceable whiteboard . The marker is done with water , about the cheapest and most environmentally friendly medium , apply with a jet printing machine . Anything printed is invisible under ordinary light , but discover itself when illuminated in ultraviolet illumination , specifically at 254 nanometers , a wavelength too unretentive even for creature , like bees , that can see in the near UV .
Once the message has been read it is gentle to prevent it fall into the wrong hands . Rather than burning the message ( permit alone have it ego - destruct ) , puff - drying the paper for 15 - 30 seconds not only score out the content but forget the paper quick to be print on again .
" The rewritable feature significantly subdue the cost . The cost per photographic print is estimated to be RMB0.014 ( $ 0.002 ) , " said senior authorDr Qiang Zhaoin astatement . " Most fluorescent surety ink on the market used to record secret information are environmentally hostile and can not be delete . The paper is only a disposable transcription medium . "
Environmental footprint may not be front of idea for those sending clandestine message , but Zhao stresses it ’s not just the ink that does well on this score . The manganese program is also low in encroachment , include in perniciousness for those handling the paper .
Like all security procedure , Zhao ’s product has a weak point . If a paper print with a mystical content falls into the amiss hands , provided they recognize the apparently white Sir Frederick Handley Page may contain a message and are aware of the applied science , they are probable to be capable to shine an appropriate ultraviolet luminance on the material and disclose its closed book .
For these cases , Zhao has got a step further , combining a suited coating with magnesium chloride and Mg bromide inks that are invisible under both sunshine and UV . In these cases only photoluminescence lifetime imaging , whose availability is limited , will give away the concealed schoolbook .
