Show glass made to protect documents from the sun an aid to the museum curators the production of document glass which is designed to protect valuable manuscripts from the deterioration teri oration caused by harmful light rays is announced says scientific american developed to meet a growing demand by museum directors and curators of collections of rare manuscripts document glass filters out the ultraviolet ultra violet portion of the spectrum exposure to which causes cause s discoloration or paper and fading of ink at the same time giving complete visibility by transmitting the visible light rays development of document glass was based on the fact that the ultraviolet ultra violet portion of the spectrum is most destructive to paper stocks and inks of various kinds as established in research activities carried out at the swedish national testing institute in stockholm the most active light rays are those beyond the range of the visible spectrum in the short wave region of ultraviolet ultra violet shorter than the milli microns after considerable experimentation with chemical ingredients designed to transmit the visible light rays and filter out the ultraviolet ultra violet document glass was perfected comprehensive tests reveal that i it transmits only 3 per cent of the invisible radiation just out of the visible range yet has a relatively very high transmission within the visible portion of the spectrum the chemical elem elements lints which give the glass its non actinic quality impart to it a very faint pink tinge which is no way interferes with visibility with the extremely low ultraviolet transmission effected by document glass by far the lowest obtainable tai with any glass of comparable iris visible i ble transmission the fading of even the most delicately colored ink and the deterioration ol 01 the paper should be almost wholly prevented |