If you smoked in the flue gas after a period of time or a circular sample color no change, can continue smoked, or rules of several cycles, or enough to make sample to produce a certain degree of color change cycle several times.
test steps ：
(1) suspension test samples and controls are arranged in the test case, and there is no direct contact between test samples and test samples and control cloth. At the same time, they cannot contact any hot metal surface. The test cloth is generally used to hang three pieces in the box evenly.
(2)lit the gas and adjust the instrument to test cases for temperature less than 60 ℃.
(3) observe the change of control cloth. Until the control cloth and standard faded cloth have obvious color difference in daylight, take out the test sample and compare the color difference with Grey Scale immediately.
(4) the samples taken out may continue to change color. If any other assessment is needed, the test sample and control sample and several original test and control cloth should be soaked in the urea solution (buffer) for 5 minutes immediately. Then it dry and rinse thoroughly, the temperature is not more than 60 ℃ dry in the air.
(5), after the first cycle, with no discoloration and the processed samples without buffer can continue to put the case back to test, hang untested control cloth at the same time, continue to test. The test sample was evaluated when the control cloth placed in the second place was significantly different from the standard fading cloth.
(6) the test cycle may need to be repeated several times until the test sample reaches the specified color difference.
