Colorfastness to atmosperic Oxides of nitrogen

This part of ISO 105 specifies a method for determining the resistance of the colour of textiles to the action of oxides of nitrogen in the atmosphere at elevated temperatures and high relative humidities.

A test specimen and a piece of control fabric are simultaneously exposed to oxides of nitrogen in an atmosphere which is maintained at 87.5 % 2.5 % relative humidity and at temperature of 40 øC 1 øC until the control fabric shows a colour change corresponding to that of a reference of fading. The exposure/measurement cycle is repeated until the specimen shows a definite colour change or for a prescribed number of cycles.
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http://www.dfmg.com.tw/member/standard/bs/BS-g04.HTM