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 fillers outtie out the ultraviolet ultra violet portion of the spectrum exposure to which causes discoloration or paper and fading of ink at tire the same time g giving lv complete visibility by transmitting the visible light rays development of docu document meni glass was based on the fact that the ultraviolet ultra violet portion of the tha spectrum Is most destructive to paper stocks and inks ot of various kinds as established in research activities carried out at the swedish national testing institute in stockholm the tha most active light rays are those beyond the range ol of the visible spectrum in the short wave region ot of ultraviolet ultra violet shorter than milli microns P after considerable experimentation with chemical ingredients designed to transmit the visible light ligh t rays and filter out the ultraviolet document glass was perfected comprehensive tests reveal that it transmits only 3 per cent of the invisible radiation just out of the visible range yet has a relatively very high transmission within t the a visible portion of the spectrum the a chemical elements which ch give the a 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 visible transmission the fading of even the most delicately colored ink and the deterioration of the paper should be almost wholly prevented |