Patent ID: 8101047

Claim:
A method of determining the amount of free water that is in a paper product that includes both gypsum and calcium carbonate fillers, which comprises the steps of: (a) measuring the amount of total water that is in the paper product; (b) calculating the amount of crystal water that is in the paper product by a process that comprises the steps of: (i) irradiating a first position on the paper product with a first X-ray having a known X-ray spectra which is sensitive to both gypsum and calcium carbonate; (ii) detecting the amount of first X-rays emitted from the paper product; (iii) irradiating a second position on the paper product with a second X-ray having a known X-ray spectra which is primarily sensitive to gypsum; (iv) detecting the amount of second X-rays emitted from the paper product; and (v) determining the amount of gypsum in the paper product; and (vi) deriving the amount of crystal water that is present in the paper product on the basis of the amount of gypsum that is in the paper product; and (c) reducing the amount of total water by the amount of crystal water to yield the free water amount that is in the paper product.