Paper takes up and gives off moisture with the surrounding air, and moisture changes thickness, strength, curl and even some optical readings. Standard conditioning holds samples at 23 degrees C and 50 percent relative humidity until they reach equilibrium, usually approached from the dry side after a drier preconditioning step. Optical tests are less sensitive than strength tests, but opacity and color still shift on very wet or very dry samples.
Those reel samples haven't conditioned yet, so the caliper numbers off the machine are just for trend.
Also heard as
- sample conditioning
Related terms
Handsheet
Laboratory-made paper sheet formed from a pulp sample under standard conditions for testing.
Caliper
Thickness of a single sheet of paper, measured under a set pressure and given in micrometers or thousandths of an inch.
Reel sample
Strip of paper torn across the full width of a finished reel for lab testing before the reel is released.