The solution is composed of—
| Asphalt | 5 | parts. |
| White wax | 6 | parts. |
| Stearic acid | 6 | parts. |
This mixture is boiled, and to it whilst boiling is added in drops a solution of two parts of soda. When cold this mixture, which is fairly hard, is dissolved in about an equal volume of turpentine, filtered and kept in bottles for use.
A sufficient quantity of this asphalt solution, which must not be sensitive to light, is poured into the middle of a levelled stone and {80} distributed by means of a lithographic ink roller, which must not be used for any other purpose but this, till the coating is absolutely even and shows a light brown colour.
When this film has become quite hard, fine parallel lines are drawn over the whole surface of the stone with a very accurate working ruling machine, by means of which from five to ten lines per millimetre can be ruled.
When the ruling is finished the stone is given a margin of wax, and quickly and evenly flooded with the following etching fluid—
| Pure nitric acid | 0·16 | parts. |
| Alcohol 36 per cent. | 0·60 | parts. |
| Water | 35 | parts. |
And, watch in hand, is etched for about half-a-minute.
Instead of the above a solution of—
| Glacial acetic acid | 2 | g. |
| Water | 100 | g. |