_Ten-Pound Paper._ This weight of paper is intended for use where one or two copies are wanted. Its weight enables it to stand the hard usage to which it is put. On one or two copies, the additional weight or thickness of the carbon paper does not affect the imprint. This class of paper is used with billing machines of all kinds. _Full Carbon Papers._ This is a paper which is coated on both sides for making a multiplicity of copies on tissue. The pieces of carbon paper are placed between _every other piece_ of tissue paper and manifold on the top of one sheet and the bottom of the next. This carbon paper is used to reduce the bulk of paper in the typewriter—one-half as much carbon paper being required. It is sometimes called _double_ carbon paper, and is mostly used by railroads in making up way bills on yellow (dandelion grade) tissue paper. _Copy Carbon Papers._ This paper is for use where it is necessary or desirable to make a carbon copy from which to make a letter-press copy. Hektograph carbons are for making carbon copies to be used in a hektograph. _Pencil Carbons._ This class of carbon paper is made in the heavy grades of paper from seven-pound to twenty-pound and is made full carbon in the seven-pound weight. _Pen Carbon._ This class of carbon paper is made in the seven-pound and ten-pound weights. _Troubles and Remedies._ Carbon papers made in summer have different treatment in the matter of color mixture than those made in winter. Users should always remember that carbon paper which has lain unused all year has gradually dried out and depreciated in efficiency. The fresher a carbon paper the better—therefore it is not economy to buy too large a supply if it is liable to stand for more than six months. Never store carbon paper near heat, nor in the direct rays of the sun. The one great difficulty experienced with carbon paper is the streaked effect called "treeing." This is caused by the carbon paper being inserted unevenly between the sheets of paper used with it. Once wrinkled, it remains so, and gives the streaked result as long as it lasts. To guard against this trouble, the operator should watch that the carbon paper is not wrinkled when inserting it between the sheets of paper, and should press the release lever on the typewriter to release the paper-feed rolls on the machine, after the paper is inserted in it, so that the unequal tension of the paper and carbon paper may adjust itself. _Durability of Color._ Black paper made of carbon pigment is indelible and most durable. Blue or purple papers are next in the order of durability of color, and are made of aniline dyes. Green next, and red next. The fact is that red and green carbon papers should not be used for permanent records, as they will fade quickly.