By fracture or examination of the grain-

Wrought Iron has a rough fibrous fracture. Good quality wrought iron has a fine fibrous fracture. Outside appearance is of a dull black colour with reddish scale.

Mild Steel has a grey-white colour with small polished grains intermixed and not fibrous like wrought iron; inclined to be granular and silky in appearance. Outside appearance is of a bright black colour.

Cast Iron has a dull grey granular appearance, and the grain varies according to the quality. The finer the grain the better the quality.

Tool Steels have a grey-white granular appearance, and the better the quality of the steel the finer the grain, until with air hardening steels the grain has a silky appearance. Outside appearance is of a very bright blue-black colour.

Shear Steels have a coarse granular appearance with white faceted grains closely mixed, and it does not break with such a clean fracture. These steels can be welded.

Burnt Iron or Steel is very brittle, coarse grained with very bright facets mixed with dull grains.

To fracture the metal, nick it with a chisel, file, or emery wheel, then break it.

Doubling Over Test

If wrought iron is doubled over on itself and then hammered flat at the bend it will partly break open and show the fibre; mild steel does not break when treated in this manner.

Drop Test

Tool Steels have a very high-toned ring when dropped on a stone floor. The harder the steel the higher the note.

Mild Steels and Wrought Iron have a lower tone and a dull ring.

Cast Iron has a very dull and dead sound.

Heat Test

Heat to a bright red and quench out in water, then try it with a file; if it cannot be filed it is carbon tool steel.

High Speed Steel can hardly be filed at all when in its natural state as it is very hard.

The methods above mentioned are rough and ready, but the necessary chemicals for testing in the proper manner are not always to hand.

Warping and Cracking of steel is caused by improper treatment when being forged, insufficient annealing (setting up internal strains), not heating thoroughly when preparing for hardening, or heating too quickly.

Warping in hardening is caused by one side of the article being cold before the other, or the thin side becoming cold before the thick side, so distorting the object.