A technical dictionary of printmaking, André Béguin.

1. GRAINING STONES.
The purpose of this operation is to create a grain on the surface of a lithographic stone (i.e. an irregular surface with small, closely-spaced bumps as opposed to a smooth surface which is brought about by pumicing and polishing). Lithographic crayon or ink wash drawings done on such a grained surface look much like drawings done on grainy paper. On the other hand, the graining done on lithographic metal plates is essential as this grain will catch the ink and water necessary for printing the impressions. Graining on metal is also done to catch the layer of light sensitive material and thus the image in photographic processes.
The graining of stones is done after planinq, pumicing, and effacing (if the stone has already been used). The effacing must be quite deep, especially if ink has been used since the ink will have penetrated quite far into the stone.
Planing, pumicing, and graining used to be done in large workshops during the 19th century, quite often with a machine. These graining machines could grain in one hour the same amount of stones it took a specialized worker to do in a day. At present graining is done by hand in workshops that are no longer on the industrial scale of the last century. The graining is done with a graining disk, (also called "levigator") which is a block of (cast) iron weighing some 25kg (55 lb). The disk is turned in figure eights, without exerting pressure, by revolving the weight around an eccentric handle. Graining can also be done by rubbing the stone surface against another stone surface. Unfortunately this manual graining is slow and hard work, especially if done on large surfaces.
In order to wear down the stone it is essential to use an abrasive such as powdered sandstone, silex, or carborundum, liberally sprayed with water. The powder must be sifted with a size 80 or 100 sieve for pumicing. The actual graining is done using very fine sand or scouring sand whose size will be progressively moved from 100 to 400. As the graining becomes finer and finer use increasingly fine measures. The grain obtained is of the same size as the last abrasive used.
The graining done stone surface to stone surface produces a fine and regular yet pronounced grain (piquant or "prickly" as the French call it). Such a grain is particularly suited to crayon work. The stone used to grain a lithographic stone must be of the same size and quality. A stone that is of inferior quality will tend to lose its edges, which is dangerous since the stone might become convex. The stone used for graining, on the other hand, tends to be worn down in the middle thus making it progressively concave. In order to compensate for these phenomenae one must exchange the stones (the bottom one being put on the top) this being done when the stones have been rubbed together until the abrasive has been quite worn down. When the abrasive is worn down the two stones tend to stick to each other since there is no longer anything to separate them. Large format stones are grained using a small stone which is moved regularly over the surface of the larger stone. After each graining (each time the size is changed) the stones must be washed thoroughly, dried with a sponge, and must be checked as to their being perfectly flat (use a metal ruler for the purpose).
The graining done with a graining disk may, at times, show scratches but, on the other hand, disks present the advantage of attacking the stone more rapidly and strongly. Furthemore, the graining disk does not stick to the stone surface and the scratches can be removed with a pumice stone.
Manual graining is done on a graining table. Such tables are very solidly made. The top part of the table is made of strong transversal bars which support the stones. Below these bars the table has sides which slope like a funnel covered with zinc or lead whose purpose it is to collect the "mud" produced by the graining and empty it through a tube into a pail. Usually graining tables are square or slightly rectangular. The larger sizes of such tables are over a meter square (9 ft2).
The graining can be finished off by pumicing with sandstone but usually such pumicing is only used to prepare the stone surface for inking and especially for drawing and making precise lines with instruments since these types of lithography are not much suited to graining.
Sandstone bricks or pure pumice should not be used to prepare the stone for inking since they will lower the grain. Soft bricks should be used in which wax and alum are mixed with the pumice. Hard bricks wear down the stone, which is unadvisable if lithographic crayons or transfers are to be used, or if picturesque lavis (wash tint) is to be done. An overly soft brick will tend to scratch the stone. [lithography].

2. GRAINING OF METALS.
Zinc or aluminium plates used in lithography must always be grained.

A. MECHANICAL GRAININC WITH BALL GRAININC MACHINES. The metal plate is fixed on a perfectly flat surface with raised edges. In the past such edges were made of linoleum. This surface is moved in a continual excentric movement (150 to 200 revolutions per minute). Balls of wood, glass, porcelain, marble, or steel are placed on the plate. The balls are sprayed with some abrasives and with water. The abrasive used may be scouring sand, sandstone, pumice stone, or, better still, zinc or aluminium.
A North American variation of this technique calls for balls with different diameters for the same metal.
When the balls have become smaller due to wear they must be replaced. When new the balls of glass or porcelain should have a diameter of 20 to 27mm (.8 to 1.1 in) and the steel balls a diameter of 12 to l5mm (.5 to .6 in). Broken balls with flat areas are dangerous as they can scratch the metal and must therefore be removed.
It usually takes anywhere from 40 minutes to one and a half hours to obtain a satisfactory grain. Once the desired result has been obtained, remove the plate carefully, wash and brush it under running water, and dry it. At this point the plate is ready for scouring (with nitric acid mixed with some alum) and for drawing upon.

B. CHEMICAL GRAINING. Graining done with acid vapours. This type of graining is done on relatively small surfaces. The plate is placed above a basin containing hydrochloric acid. The emanations of the acid provoke, after some ten minutes, a regular and quite fine graining. The plate is then washed with water and quickly dried.
In case the plate does not need a very fine grain one can also wash the plate in a solution of caustic soda, rince it with water and follow up by pumicing with a flannel dabber impregnated with fine emery powder or carborundom. [abrasives substances, attacking agents].
In the case of transfer or crayon work the graining can be first done with a chemical "etch" and then be followed up by rubbing the plate with fine pumice. This will produce a very fine grain. The next step is to wash the plate and dry it with a clean rag, a hair drier, or a fan.
Chemical graining is quite light but it presents the advantage of dispensing with any particular equipment. It can be done on both zinc and aluminium plates.
Other chemical graining processes exist, such as attacking zinc plates with a hot solution of phosphate or chlorates, fluorates, and chromates. Aluminium can also be oxydized by electrolysis of aluminia.

C. GRAINING WITH SAND BLASTING. The plate to be grained is placed on a revolving surface enclosed in a cylinder. An abrasive (carborundum for deep grainings and glass dust for lesser graining) is blown by nozzles which move laterally. This kind of graining process is very clean, relatively silent, and results in a regular grain. The size of the grain is regulated by changing the angle of the various jets. The abrasive jet may be either dry or wet depending on the machine used. After graining the plate must be carefully brushed and washed with water and then properly scoured in order to eliminate any bits of abrasive that might have gotten stuck in the hollows of the plate surface.

The graining done on intaglio plates causes the surface of the plate to be covered with little holes that are more or less regularly spaced. The holes will catch the ink when the plate is inked and even after wiping. After printing the result of this graining will be a kind of dotted pattern that can be compared to the effect of a screen. This is in opposition to using lines to express tints and half-tone's. There are several methods of graining a plate but these methods are described in the article on granulated plate surfaces.
There are two basic types of graining: positive graining and negative graining. The first of these consists in making little holes through an acid resist or a ground which, when bitten, will create little holes on the plate surface itself. Once the biting is done all that is left to do is to ink these hollows and print a black grain on a white background. Negative graining, on the other hand , consists in depositing on the plate surface particles of an acid resistant substance (resin, asphaltum, varnish, or paint) which will protect the plate in those particular areas during biting. Hollows thus appear around the protected areas which remain in relief. After impression the protected areas will show up as a white grain on a black background.
Positive graining is done by depositing powdered substances (that will soak up water) into a layer of warm ground covering the plate surface. The next step is to plunge the plate into water, which causes the varnish layer to crack in those places where the water receptive grains were deposited.
Negative graining can be done by depositing dry resin or asphaltum dust on a plate and then fixing it to the plate by heating. Another way is to cover the plate with alcohol mixed with resin dust. The resin settles on the plate as the alcohol evaporates. In this second manner the plate must also be heated to fix the resin dust. Yet another way of graining negatively is to vaporize varnish or acrylic paint with an airbrush.
These various ways of graining are described in greater detail in the articles on aquatint, the dust-box, and grain.

The phototype process depends on the property of bichromated gelatine to retain greasy inks where it has been exposed to light and to accept only water on the areas where it has not been exposed. In the Albert process (Albertype) the gelatine is poured onto a glass plate. Graining is done in order to ensure the adhesion of the gelatine to the glass. This kind of graining is done is a rectangular wooden basin which stands on four legs. The glass plate is put in the basin (face side up) where it is held down by a batten and dusted until a good layer of fine emery has been built up. In order to obtain the required abrasive paste add some water to the emery powder. At this point put a second glass plate onto the first one, making sure that the face side is pointing down. Then rotate the top plate pushing down with both hands. Care must be taken that the two plates are perfectly parallel to each other. Every once in a white switch the top plate around so that the graining will be regular. Continue for some ten minutes then exchange the plates so that the one below is above and vice-versa (this will also ensure the regularity of the graining). After another ten minutes separate the plates carefully, sliding them away from each other since by now they will tend to stick together. Then wash the two plates with a clean sponge under a jet of water and dry them.