30 DIES FOR STAMPING 



correctness, by impressions in clay, and dabs, or casts in type-metal, the die is ready 

 for tho important operation of hardening, which, from various causes, a few of which 

 will be enumerated, is a process of much risk and difficulty; for should any accident 

 now occur, the labour of many months may be seriously injured, or even rend, red 

 quite useless. 



The process of hardening soft steel is in itself very simple, though not very easily 

 explained upon mechanical or chemical principles. We know by experience that, it 

 is a property of this highly valuable substance to become excessively hard, if heated 

 and suddenly cooled ; if, therefore, we heat a bar of soft malleable and ductile steel red 

 hot, and then suddenly quench it in a largo quantity of cold water, it not only becomes 

 hard, but fragile and brittle. But as a die is a mass of steel of considerable dimen- 

 sions, this hardening is an operation attended by many and peculiar difficulties, more 

 especially as we have at the same time to attend to the careful preservation of the 

 engraving. This is effected by covering the engraved face of the die with a protecting 

 face, composed of fixed oil of any kind, thickened with animal charcoal : some per- 

 sons add pipe-clay, others use a pulp of garlic, but pure lamp-black and linseed-oil 

 answer the purpose perfectly. This is thinly spread upon the work of the die, which, 

 if requisite, may bo further defended by an iron ring ; the die is then placed with its 

 face downwards in a crucible, and completely surrounded by animal charcoal. It is 

 heated to a suitable temperature, that is, about cherry red, and in that state is taken 

 out with proper tongs, and plunged into a body of cold water, of such magnitude as not 

 to become materially increased in temperature ; here it is rapidly moved about, until 

 all noise ceases, and then left in the water till quite cool. In this process it should 

 produce a bubbling and hissing noise ; if it pipes and sings, we may generally appre- 

 hend a crack or fissure. 



No process has been found to answer better than the above simple and common mode 

 of hardening dies, though others have had repeated and fair trials. It has been pro- 

 posed to keep up currents and eddies of cold water in the hardening cistern, by means 

 of delivery-pipes coming from a height ; and to subject tho hot die, with its face 

 uppermost, to a sudden and copious current of water, let fall upon it from a large pipe, 

 supplied from a high reservoir ; but these means have not in any way proved more 

 successful, either in saving the die, or in giving it any good qualities. It will be recol- 

 lected, from the form of the die, that it is necessarily only, as it were, case-hardened, 

 the hardest strata being outside, and the softer ones within, which envelope a core, 

 something in the manner of the successive coats of an onion ; an arrangement which 

 we sometimes have an opportunity of seeing displayed in dies which have been smashed 

 by a violent blow. 



The hardening having been effected, and the die being for the time safe, some fur- 

 ther steps may be taken for its protection ; one of these consists in a very mild kind of 

 tempering, produced by putting it into water, gradually raised to the boiling point, 

 till heated throughout, and then suffering it gradually to cool. This operation renders 

 tho die less apt to crack in very cold weather. A great safeguard is also obtained by 

 thrusting the cold die into a red-hot iron ring, which just fits it in that state, and which, 

 by contracting as it cools, keeps its parts together under considerable pressure, pre- 

 venting the spreading of external cracks and fissures, and often enabling us to employ 

 a split or die for obtaining punches, which would break to pieces without the protecting 

 ring. 



If the die has been successfully hardened, and tho protecting paste has done its duty 

 by preserving the face from all injury and oxidisement, or burning, as it is usually 

 called, it is now to be cleaned and polished, and in this state constitutes what is 

 technically called a matrix ; it may of course be used as a multiplier of medals, coins, 

 or impressions, but it is not generally thus employed, for fear of accidents happening 

 to it in the coining press, and because the artist has seldom perfected his work upon 

 it in this state. It is therefore resorted to for the purpose of furnishing a punch, 

 or steel impression for relief. For this purpose a proper block of steel is selected, of 

 the same quality, and with the same precautions as before, and being carefully annealed, 

 or softened, is 'turned like tho matrix, perfectly true and flat at tho bottom, and ob- 

 tusely conical at top. In this state, its conical surface is carefully compressed by 

 powerful and proper machinery upon tho matrix, which, being very hard, soon allows 

 it to receive the commencement of an impression ; but in thus receiving tho impn .-- 

 sion, it becomes itself so hard by condensation of texture us to require during tho 

 operation to be repeatedly annealed, or softened, otherwise it would split into Miiall 

 superficial fissures, or would injure the matrix ; much practical skill is therefore re- 

 quired in taking the impression, and tho punch, at each annealing, must bo carefully 

 protected, so that the work may not be injured. 



Thus, after repeated blows in the die-press, and frequent annealing, tho impression 

 from the matrix is at length perfected, or brought completely up, and havin 



