A technical dictionary of printmaking, André Béguin.

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Abrasive Substances.
Substances able to wear down or polish other ones by means of rubbing one against the other. In the past sandstone and pumice stone were the most commonly used, in powder or solid form, as well as stones of varying hardness.
Today, other harder minerals are used such as silex or powdered quartz (the latter being white), silicates (silica plus metal) which are a brownish-red colour, emery, which is black, aluminium oxyde, which is black and very hard (the trademark "Carborundum" uses this substance), as well as ground glass. Abrasives can be found in solid form (stone, brick, etc.) or as a powder, in which case the powder is regularly distributed over and glued onto paper or cloth (either permeable or impermeable), onto disks, strips, plates, brushes, belts, etc. The grain of the abrasive may be either extremely fine or very large. A large grain facilitates the dispersion of the powder produced by rubbing. Abrasives should be kept in a relatively dry place that is not too warm. Depending on the use to be made of abrasives they can be used dry, with water, with oil, with petroleum, with soap or with special products.
Abrasive powders are calibrated and. subdivided according to the table given below.

USING ABRASIVES.
A. CLEANING METAL PLATES. (removing rust, stripping, equalizing, cleaning tools and plates). For this kind of work one may use either emery cloth or abrasive paper with a sanding machine or by hand. If, however, the work is to be done by hand one should use a rigid support (a piece of wood, for example) so that the sanding is done evenly and produces a flat surface. For the initial rough work a dry sanding may be done but for finishing up a sprinkling of water or petroleum should be used. This last stage may be carried out, making sure that a flat surface is being produced, with the addition of some oil. If one wishes to plane a small plate, this can be done by rubbing the plate on a sheet of sandpaper that has been fixed to the work table. The movements for such work should be regular and of small scope. Lowering the entire surface of a plate necessitates a dry process.
B. SHARPENING TOOLS. Carborundum paper of a middle, fine, or very fine grain should be used to make the edges on the tools but it must be used dry. Sharpening may be done with the same paper and petroleum, and finally finished off by adding oil. It is, however, best to use a fine stone to set up tools .
C. POLISHING OF METAL PLATES.The initial rough work may be done by dry sandpapering with medium or large grained paper depending on the condition the plate is in. The scratches left by an abrasive substance must always be smaller than the ones one wishes to remove. If the plate being worked has not been overly damaged one may begin with grade 120 sandpaper and then move on to grades 220, 400, 600 and finish off with steel wool. Sanding should be done with a circular movement so as to eliminate any scratches. The abrasive should be attached to a flat piece of wool(?) so as to prevent the sandpaper from following the plate's hollows, ridges, etc.
Finishing off may be done under a trickle of water or with some oil. If one uses a sanding machine the job can be done much more quickly than with brushes, disks, or plates. At the end of this operation add (for steel with a high carbon content) some mineral oil emulsion. For steel that has a low carbon content as well as for nickel and chrome plates it is best to use solid grease or a soluble oil. If the plate to be treated is of a non-ferrous material one may use mineral oil or even water to which chalk has been added. To give the finishing touches jeweler's abrasives and polishing liquid may be used as well as stones, to make the plate brilliant, and soap.

GRAIN OF ABRASIVES:

Grain

Old system

Sizes

Simplified system

Silex

Emery

ROUGH WORK

very large

grain

4 1/2
4
3 1/2
3
2 1/2

12
16
20
24
30

very large

3

2 1/2

PUMICING

large

2
1 1/2
1

36
40
50

large

2

1 1/2

MEDDLING WORK

middling

1/2
0
2/0

60
80
100

middling

1

1/2

FINISHING UP

fine

3/0
4/0
5/0

120
150
180

fine

0

2/0

POLISHING

POLISHING

SHINING

very fine grain

6/0
7/0
8/0
9/0
10/0
11/0
12/0

220
240
280
320
360
400
500
600
800
1200

very fine

3/0

4/0

steel wool

emery powder


SPEED OF SANDING MACHINES

SYSTEM

STEEL

COPPER, ZINC, ALUMINIUM, BRASS

BELT

3500 to 5000 r.p.m.

4500 to 7500 r.p.m.

DISK, WHEEL

5000 to 6000 r.p.m.

5000 to 7000 r.p.m.

POLISHING WOOD.
When working on wood use dry crushed-glass paper. The surface of a piece of wood to be used for engraving must be rubbed with caution and, in the case of wood for woodcuts, rubbing must be done in the direction of the grain. In fact, abrasives tend to break wood fibre and in order to avoid this problem wood blocks are best prepared with a plane. In any case use only fine abrasives that are well spaced and fixed onto perfectly flat planes. For soft woods one uses aluminium oxyde with a widely-spaced grain. Painted and varnished woods should be wetted with soapy water.
E. POLISHING PLASTIC.
Use a fine or a very fine carborundum abrasive paper and wet the plate abundantly with water or oil. Rub the surface smooth, quite slowly, without applying any pressure.
F. ENGRAVING.
The abrasives used in engraving are powdered ones or on sheets and are used to obtain grainy textures or gray printing plates [*grays]. This is usually achieved by rubbing the plate, by passing the plate through the press (abrasive side resting on the plate), or by using a carborundum crayon to grain.
G. LITHOGRAPHY.
Rough work and graining are done with a hard, powdered abrasive such as sandstone or carborundum which are wetted and crushed. Pumicing* and polishing*, whose aim it is to soften the stone, must be done with fine abrasives such as pumice or sand.


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