Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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opacity

That property of a material which restricts the passage of light and thus prevents one from seeing through it or seeing objects on or in contact with the reverse side. Opacity is of considerable importance in paper that is to be used for printing. Tn printing papers opacity is measured in percentages. e.g., a lightweight bond paper may have an opacity as low as 79%, i.e., 21o of the light that strikes it passes through, while a 24-pound bond paper of high opacity may rate a percentage of 93, meaning that only 75 of the light penetrates it. Different opacities may be obtained by: 1) varying the paper pulp; 2) varying the degree of hydration; or 3) using loading materials and special opacifying agents. (17 , 350 )




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