Procure three small triangular files, sold at fourpence each. Break an inch off the end of them, and grind them with emery on the lead lap into a pyramidal point ([Fig. 7]), with edges as keen as a razor and point sharp as a needle’s. Set up the ‘slitter’ (the disc and its spindle) in position, taking care that it stands truly perpendicular. Then arrange a wooden rest underneath the edge of the disc nearest to you, as shown in [Fig. 7]. The support must be securely fixed, and of the exact height to enable the disc to revolve upon it. Wet the edge of the disc, and turn the handle N with the left hand. Take a file and fix its point into the wooden rest, so that a keen edge may catch the edge of the revolving disc. This will take off a shaving of iron wherever it bites, and by degrees the edge of the disc will be turned true, and continuous shavings will curl off it. There is nothing difficult about this. It requires a neat hand, and you may want to use three files before finishing; but when you understand that you require the edge of the disc to be perfectly true you will soon attain the result; and by lightly applying the file to the upper and under surface of the edge of the disc you will remove any roughness caused by the turning, and the disc will be ready for use.
Remove the wooden support. Put a common plate under the slitter to catch the paraffin, which will shortly require notice.
The disc has now to be CHARGED WITH DIAMOND. This sounds somewhat alarming, but take courage. Diamond ‘bort’ consists of genuine diamonds not sufficiently good to be used for gems. It may be bought of any of the ordinary merchants at a cost of about six shillings the carat. That amount would be enough to cut about twelve or fourteen pebbles an inch and a half in diameter. This is the only serious expense when once the bench has been set up and furnished. And after all it is not very formidable. Take a fragment of bort, and crush it upon a piece of hard steel by means of a steel rod one inch in diameter and six inches in length. Put the bort on the steel plate; smear a little butter over the bort to prevent the broken pieces flying away. Hold the steel rod upon it, and give it a smart blow with a hammer. This crushes the diamond. Then pound it into the smallest possible powder, using the steel rod as a pestle.
Fig. 8.
Now pour some paraffin into a saucer (J, [Fig. 8]), and with a feather smear paraffin over the edge of the disc revolving slowly. Take some of the powdered diamond on the forefinger of the right hand, and very carefully transfer it to the edge of the disc. The entire edge must in this way be anointed with crushed diamond-dust. Then a smooth pebble is taken in the right hand (the hand resting comfortably on a support G), and pressed against the edge of the disc revolving. Let us understand exactly the object and action of this. The diamond-powder is the hardest known substance in Nature; the disc is of soft iron; the flint pebble is very hard. By the process just described we press the diamond-powder into the substance of the disc, so that the edge becomes armed with grains of adamant; the edge becomes a mighty file, or an irresistible saw. The principle is so simple. When you have driven sufficient diamond-powder into the edge of the disc, you have invested the iron with an armature which can cut through every hard substance that exists in Nature except the diamond itself. The hardest flint, emery, iron, glass, metals, etc., must all bow beneath its mighty power. I should like to shake hands with the man who devised this simple and clever method. Before its invention agates kept their treasures locked in close caskets. The diamond-toothed ‘slitter’ has supplied the key for unlocking their secret beauty.
Well, now, the disc is CHARGED, and if you wish to proceed like most of the lapidaries do, you will take the pebble you wish to cut between the forefinger and the thumb of the right hand, letting it rest on the second and third fingers. You will place the support in position, that the hand may rest comfortably upon it when holding the pebble against the disc; and you will begin turning with the left hand. You will soon see that the disc has begun to cleave its path. A distinct cut is visible. You must keep feeding the edge with paraffin by means of the feather; and as, unfortunately, you have not got a third hand, you must hold the feather between your teeth, or else get a friend to do the turning. It ought to take about half an hour to cut an inch through a pebble two inches in diameter. The disc will have to be re-charged with diamond occasionally, which may be done by using the slit of the pebble you are cutting as a ‘charger.’
Such is the method of cutting in vogue among most lapidaries. It answers very well for professionals, but it certainly presents more than one objection to amateurs. I found the objections so weighty that it required no small determination to persevere. First of all, it is very difficult to hold the stone true, so that the cut shall proceed in the same straight line; then the paraffin and detritus of the cutting cause such a disagreeable ‘mess,’ in which the right hand has to take up permanent quarters, and the nuisance of feeding the paraffin by holding the feather in the mouth is very great. Finding these objections a grave impediment to success, I bethought me of a device I once saw used by a lapidary, and improved upon it in design, and got a tool made by Mr. Moore, of Clerkenwell, which has proved the greatest comfort and most complete success, entirely obviating all the disagreeables alluded to above. The diagram ([Fig. 8]) ought to make it clear to you.
A B is a circular steel rod, with shoulder at B, and screwed underneath, rising ten inches above floor of bench. It has an arm (C D) moving easily round, which can be set at any height by screw and nut (E). At D is a hole large enough to admit the cement-stick with pebble attached. This is held securely by a screw at D. A string (F) is slipped over the cement-stick just above the pebble, with a weight attached to the other end. The string passes over a pulley (G) in the opposite side of the bench. It is obvious that the weighted string will always keep the pebble with even pressure against the disc. The result is that all difficulty in holding the pebble is removed. The pressure is constant, and the cut is made perfectly true. The right hand is now free to manipulate the feather for lubricating the disc, and you can work without getting a drop of oil upon your fingers. You turn the handle as briskly as you like. The large wheel multiplies the reel ten times—i.e., one revolution of the handle produces ten revolutions of the disc. I often attain a speed of fifteen hundred revolutions of the disc in a minute when cutting a pebble! Keep all points of friction well oiled, and everything will go merrily as a marriage bell. H shows the plate for catching the drops of paraffin and detritus from the stone; J shows the saucer of paraffin. The length of the arm (C D) is ten inches. When you want to recharge the disc with diamond, lift the weight at end of string, shift the arm and the stone to the right, feed the edge of the disc with diamond, and drive it in with a smooth stone as before described.
When your stone is cut through wash the halves, and remove the cement by heating over a candle. The same cement will do for many stones.