Paper dulls knives relatively fast for its volume. Typically we only cut a small volume of paper so it is not very noticeable. I almost never use scissors when I can use my pocket knife. When you do this you notice dulling. A common example of this dulling is to observe how fast Xacto knives used for doing paste-ups get dull.
Clay is a standard component of paper. The amount varies. It can be really surprising when you look at magazines:
"MOST MAGAZINES are printed on coated groundwood paper, which is the same kind of paper used by newspapers. Clay, the most common coating, smoothes the surface of the paper and creates a surface glossy inks can adhere to. A two-sided, coated paper sheet used for magazines will normally have 30 to 35 percent clay and filler and 65 to 70 percent paper fiber content."
Here is a little more info on minerals used in paper making:
"The most generally used filler is clay, which is a natural white mineral, formed by the weathering of certain types of rock. It is prepared for use by washing, separating sand and mica, and drying for shipment. Formerly much of the clay came from England, but the greater part now used in this country is of American origin. The important properties for a filler clay are good whiteness and freedom from grit and mica. Particle size is not nearly as important as in a coating clay and little attention is paid to this property in selecting a filler. Uniformity of color is also not as important as in coating clays because the filler is dispersed among the fibers and its effect is much less marked than when in a surface coating. This does not mean that the properties of a filler clay are unimportant and need not be controlled, but merely that they are less critical than for coating work.
In the early days clay was added dry to the stock in the beater, being measured by weight or more roughly as so many buckets full. Modern practice is to prepare a clay slip by mixing with water, adjust its dry clay content to a definite and constant value, and measure this to the beater by volume. In either case it is customary to add the clay fairly early in the beating process on the theory that if beaten into the fibers as they are cut and fibrillated its retention would be greater as the sheet is formed on the paper machine wire. It is very doubtful if this point is of any importance. No mat-ter how the stock is prepared a certain amount of the clay or other filler passes through the wire with the water, but much of this is later recovered in the white water save-ails and used over again.
The filler next in importance to clay is precipitated chalk, which is calcium carbonate. The natural ground mineral is seldom used and the manufactured product is made in several different ways and in very different degrees of fineness. Chalk is much whiter than clay and is of more help in increasing the opacity of the sheet. It is an alkaline material and its presence makes it extremely difficult to size the paper with rosin and alum. Because its alkalinity overcomes the acidity of the alum used in the beater contents, the permanence of paper filled with chalk is far greater than of that filled with clay and made acid with alum. Chalk was first extensively used in cigarette papers, which are often very heavily loaded with it, but its use in printing papers is now quite general.
Calcium sulfate in the form of ground gypsum, or more often artificially prepared as "pearl hardening," "crown filler," or material sold under some other trade name, is sometimes employed as a filler. Its crystalline form and transparency make it of doubtful value in improving the opacity and color of the paper, and its moderate solubility in water makes it of questionable economic value."
