132 Report onthe Art of making fine Cutlery, 



diftingulflicd from one of ordinary value, excepting tliofc derived from the a£i;ual ufe of 

 both: that the Turkey ftone cuts fad, but is never found with a very fine grit : that the 

 yellow hone is moft generally ufeful, and that any ftone of this kind requires to be foaked 

 in oil, and kept wet with that fluid, or otherwife its effects will be the fame as that of a 

 coaifer ftone under the better treatment : and laftly, that there is a green hone found in 

 the old pavement of the ftreets of London, which is the beft material yet known for finifli- 

 ing a fine edge. , 



The grindftone leaves a ragged edge, which it is the firft effefl: of whetting to reduce fo 

 thin, that it may be bended backwards and forwards. This flexible part is called the wire, 

 and if the whetting were to be continued too long, it would break off in pieces without 

 regularity, leaving a finer, though ftill very imperfefl edge, and tending to produce acci- 

 dents while lying on the face of the ftone. The wire is taken off by raifing the face of the 

 knife to an r.ngle of about 50 degrees with the furface of the ftone, and giving a light 

 ftroke edge foremoft alternately towards each end of the ftone. Thefe ftrokes produce an 

 edge, the faces of which are inclined to each other in an angle of about loO degrees,' and 

 to which the wire is fo flightiy adherent, that it may often be taken away intire, and is 

 eafily removed, by lightly drawing the edge along the finger nail. The edge thus cleared 

 is generally very even : but it is too thick, and muft again be reduced by whetting. A finer 

 wire is by this means produced, which will require to be again taken off, if for want of 

 judgment, or delicacy of hand, the artift fliould have carried it too far. But we will fup- 

 pofe the obtufe edge to be very even, and the fecond wire to be fcarcely perceptible. In 

 this cafe the laft edge will be very acute, but neither fo even nor fo ftrong as to be durably 

 ufeful. 



The finifh is given by two or more alternate light ftrokes with the edge flanting fore- 

 moft, and the blade of the knife raifed, fo that its plane forms an angle of about 28 degrees 

 with the face of the ftone. This is the angle which by careful obfervation and meafure- 

 ment, I find Mr. Stodart habitually ufes for the fineft furgeon's inftruments, and which he 

 confiders as the beft for razors, and other keen cutting tools. The angle of edge is there- 

 fore about 56 degrees. 



The excellence and uniformity of a fine edge may be afcertained, by its mode of opera- 

 tion when lightly drawn along the furface of the Ikin, or leather, or any organized foft 

 fubftance. Lancets are tried by fuffering the point to drop gently through a piece of thin 

 foft leather. If the edge be exquifite, it will not only pafs with facility, but there will not 

 be the leaft noife produced, any more than if it had dropped into warer. This kind of 

 edge cannot be produced, but by performing the laft two or more ftrokes on the green 

 hone. 



The operation of ftrapping is fimilar to that of grinding or whetting, and is performed 

 by means of the angular particles of fine crocus, or other material bedded in the face of the 

 ftrap. It requires lefs fliill than the operation of fetting, and is very apt, from the elaftL- 

 •Ity of the ftrap, to enlarge the angle of the edge^ or round it too much. 



Thoughts, 



