Glass Furniture Making

Originally crushed sand was used, hence the familiar name 'sandpaper', but the grit is now powdered glass, preferably from old gin or beer bottles. Slow cutting, relatively soft and soon exhausted glass is mainly used for cutting down old paint-work, although it is also used for wood finishing as it does not scratch. The flour grade 00 is still a favourite with french-polishers.

32 Abrasives (sanding paper), detail

32 Abrasives (sanding paper), detail

Flint

A natural abrasive used for hand-sanding and only slightly harder than glass, it has now been largely superseded by faster materials; moreover flint-dust embedded in the grain of sanded surfaces (cheap plywoods, etc.) has been found to cause a chemical reaction with synthetic finishes.

Garnet

Crushed garnet is used almost entirely for sanding wood. It is much harder than glass or flint, cuts quicker, lasts longer, generates very little heat and consequently rarely burns the wood. It remains a favourite material among cabinet-makers, as it yields a very smooth finish.

Aluminous oxide (Aloxite)

An impure oxide of aluminium manufactured from bauxite; the purest forms yield sapphires. rubies and Oriental topaz. The toughness and hardness of this material ensure that the individual grains will not disintegrate under the considerable mechanical strains of high sanding pressures; therefore it can be used to cut harder and faster than other materials. The white is the purest form and is usually dyed orange and reserved for wood finishing, with the impure forms of brown and pink for metals, etc. Occasionally these coarse-cutting impure forms are dyed black.

Silica carbide

The hardest and most expensive grit, produced by heating mixtures of coal and quartz in an electric furnace, and commonly known as 'carborundum. Scarcely less hard than the diamond, its sharp yet even crystalline formation is eminently suitable for wet or dry grinding, and polishing of very hard substances with a compact surface, i.e. cellulose, polyester, paint, glass, plastics, stone, non-ferrous metals, etc. It is, however, more brittle than aluminous oxide, and the latter is to be preferred for wood finishing.

Grading of papers (grain or grit sizes)

Hitherto, papers were marked with the grade only, and the principle is still employed for glasspapers which range from 'Flour', 00, to 'Strong 2"; but the grading of other papers has now been standardized to the actual mesh size per square inch for grits within the range 800, which is the finest obtainable, down to 12, which is the coarsest. To avoid confusion most papers are clearly marked with both grade and grit size, and the following table gives the various equivalents together with the approximate comparable gradings in flint- and glasspaper.

Approximate comparable gradings in flint- and glasspaper

Grit size

Equivalent

Flint-paper

Glass-

grade

paper

500

12/0

400

11/0

360

10/0

320

9/0

280

8/0

240

7/0

220

6/0

4/0

180

5/0

3/0

Flour

00

150

4/0

2/0

0

120

3/0

0

1

100

2/0

1/2

1V2

90 )

1 1

Fine

80 (

0

11/2

2

60

1/2

2

Middle

2

50

1

21/2

Strong

2

40

11/2

3

36

2

30

21/2

24

3

12

Both aluminous oxide and silica carbide papers are available in all grits up to 800, and garnet-paper up to 500 grit. The equivalent values for flint-papers are fairly correct, but glasspaper values are an approximation only, for it must be borne in mind that the harder the grit the sharper the crystalline facets and the quicker the cut; therefore there is no exact comparison.

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