To test paper for durability, tear a sheet in halves. Put one half in a dark drawer and the other.in sunlight. After two weeks compare the color, and test for strength on the Mullen tester. (The Mullen tester is an apparatus for test ing the strength of paper.) To test the sizing, touch the paper to the tongue and note if the moisture is quickly absorbed or remains on the surface ; or make a wide line on the paper with pen and ink, and when the ink is dry examine the edges of the line and the reverse side of the paper, to note if the edges of the line are sharper or if the ink soaks thru.
To detect clay in paper, burn a piece and rub the ashes in the fingers. What happens? To detect dirt, hold the sheet before a light and mark each spot ; count the spots and compare with a standard sample of same grade and size.
To judge of the formation of a sheet, hold it to the light and look thru it, or tear it in different places and both ways of the sheet. If properly made, the sheet will tear evenly and not look cloudy.
To judge if a sheet will "fuzz" in printing, rub it with the coat sleeve and look across it toward the light. If it is
"fuzzy" the fibres will be plainly seen standing on the edge on the surface. (This test is not infallible. There arc papers that are difficult to print on, on account of the "fuzz," but which endiire this test successfully.) To determine the way the "grain" runs, cut two strips one half an inch wide by eight inches long; cut one lengthwise the sheet and one crosswise. Lay one on the other and hold by one end between the thumb and finger, and note if the top strip supports its own weight or rests on the under strip. Reverse them. The strip cut with the grain will show itself stronger ; that cut across the grain will sag more.
Strength of paper may be judged by tearing it, but it can only be satisfactorily determined by using a tester such as Mullen's.
To judge the opacity of paper, lay two sheets over printed matter and note thru which the type can be more plainly seen.
To judge of the finish look across a sheet held level with the eyes.
To find the thickness of a sheet, and to estimate its "bulk ing" quality, fold it twice and measure it in the micrometer gauge.