Report on tTie Art of ma^iti^ fine Ctittny, l^t 



pofition, as well as the method by an acid which hns before been explaJneJ in this work • ; 

 and fecond, that the deep colour being obfcrved to come on firft at the thickeft parts, Mr. 

 Stodart was difpofed to think, that its more fpeedy appearance was owing to thofe parts not 

 having been hardened. But upon trial with a plate of fteel made quite hard at one end, and 

 left (oft at the other, I found that heat applied in the middle produced the regular changes 

 at both ends precifely in the fame manner. I fuppofe, therefore, that the thicker parts 

 finking deeper into the hot metal, experienced a flronger re-a£lion and better contaft, 

 which may have accelerated the communication of heat. It may be here noticed, 

 that we found upon repeating the experiment of applying nitrous acid to bright fteel, whicli 

 was hardened in part only, the black tinge appeared more fpeedily and ftrongly upon the 

 hard parts, than the reft of the furface : a remarkable event, for the explanation of which 

 I have no theory to offer. 



Let us now fuppofe our cutting inftrument to be forged, hardened, and let down ot 

 tempered. It remains to be ground, polifhed, and fet. The grinding of fine cutlery is 

 performed upon a grindftone of a fine clofe grit, called a Bilfon grindftone, and fold at tlic 

 tool fhops in London at a moderate price. The cutlers ufe water, and do not feem to 

 know any thing of the method by tallow f. The face of the work is rendered finer by fub- 

 fequent grinding upon mahogany cylinders, with emery of different finenefs, or upon cy- 

 linders faced with hard pewter, called laps, which are preferable to thofe with a wooden 

 face. The laft polifh is given upon a cylinder faced with buff leather, to which crocus, or 

 the red oxide of iron is applied with water. This laft operation is attended with confider- 

 able danger of heating the work, and almoft inftantly reducing its temper along the thin 

 edge, which at the fame time acquires the colours of oxidation. 



The fetting now remains to be performed, which is a work of much delicacy and ikill: 

 fo much fo indeed, that Mr. Stodart affures me, he cannot produce the moft exquifite an4 

 perfect edge if interrupted by converfation, or even by noifes in the ftreet. The tool is 

 firft whetted upon a hone with oil, by rubbing it backwards and forwards. In all the pro- 

 ccffes of grinding or wearing down the edge, but more efpecially in the fetting, the artift 

 appears to prefer that ftroke which leads the edge according to the action of cutting, in* 

 ftead of making the back run firft along the ftone. This proceeding is very judicious; for 

 if there be any lump or particle of ftone, or other fubftance lying upon the face of the 

 grinder, and the back of the tool be firft run over it, it will proceed beneath the edge, and 

 lift it up, at the fame time producing a notch. But on the other hand, if the edge be 

 made to move foremoft, and meet fuch a particle, it will Hide beneath it and fuffer no 

 injury. Another condition in whetting is, that the hand ftiould not bear heavy : becaufe 

 it is evident, that the fame ftone muft produce a mone uniform edge if the fteel be worn 

 away by many, than by few ftrokes. It is alfo of effential importance, that the hone itfelf 

 fliould be of a fine texture, or that its filiceous particles fliould be very minute. Mr. 

 Stodart informs me, th^at there are no certain criterions by which an excellent hone can be 



• Philofophical Journal, I. 470. \ Philofophical Journal, I. 131. 



S 2 diftin- 



