Some lapidaries, after smoothing their stones on the sand lap employ an elm lap with powdered pumice-stone, and dispense with the pewter lap altogether, facing the stone on the felt lap with putty powder. This process is advantageous in polishing stones all over. But on carefully comparing the systems I am convinced that there is nothing like the pewter and rottenstone for general purposes; though the felt is advisable for round stones when they are to be polished over the whole surface. As you proceed you will be able to try experiments at your discretion.
To polish flat surfaces of pebbles we work exactly as we have described, the only difference being that you work the stone flat on the margin of the laps. If you thoroughly understand the principle you will find the flat surfaces easier to manage than the round.
Mussel and other sea-shells, snail-shells, etc., may be polished in the same way—only that being soft they will not require the emery lap. Work them on the sand lap and cloth lap, and a little experience will soon make you proficient in the art.
IV.—HOW TO CUT A PEBBLE.
We have reserved the process of CUTTING a pebble till the last, because it is advisable to understand the polishing process first. Many pebbles make most attractive specimens without being cut, but no pebble looks well after it is cut unless it be also polished. Therefore the polishing is the first essential, and I hope you thoroughly comprehend its principles and are enthusiastic about the whole subject.
To cut a pebble, with a view to polishing its inner surface, we want a spindle and reel as before, fitted with a disc of the thinnest soft iron. These discs are of particular make, and must be procured from a practised maker. You should get six of them, ten inches in diameter, from Mr. Oxley, 83, Caledonian Road, Islington, N. The shoulder for the disc to rest on should be about five inches from the upper point of the spindle, and the nut must be screwed home very tight to keep the disc in position. The disc is ‘panned,’ i.e., beaten into a saucer-shape so shallow as to be hardly perceptible to the eye. This precaution is necessary to ensure the edge of the disc being true, for otherwise it would be impossible to make such thin iron free from undulations in the edge.
The discs are by no means cut true when sent down, and as they must be brought to absolute perfection of truth before they can be used, the first thing will be to turn the edge true.
Fig. 7.