\ 



MttmifdctureofT'm-Pfate. 145 



Some nicety, however, is required in this operation, for if they 

 remain too long in the acid, they will become stained, or blis- 

 tered by it, as the workmen term it; but practice enables a 

 careful operator to judge of the time when they ought to be re- 

 moved. This, however, is one of the most difficult parts of the 

 business, as few men like to work in it ; though I understand 

 that a good pickler is highly valued by his employers, and ob- 

 tains great wages. It is necessary to notify that this, and the 

 former process with the acidulated water, are both hastened by 

 giving to those menstrua an increase of temperature — and this 

 is effected by means of heated flues which run under each 

 trough. Little additional heat is necessary in summer, how- 

 ever, as 90° or 100° of Fahrenheit is a temperature sufficiently 

 high for either of these operations. 



When the plates come out of the pickle, they are put into 

 pure water, and scoured in it with hemp and sand, to remove 

 any remaining oxide, or rust of iron, that may be still attached 

 to them, for wherever there is a particle of rust, or even dust 

 upon them, there the tin will not fix; and they are then put into 

 fresh water to be there preserved for the process of tinning. 

 The design of putting the plates into pure water, after they come 

 out of the sours, is to prevent their becoming again oxidated — 

 for it has been found that after these operations, they will ac- 

 quire no rust, although they should be kept twelve months im- 

 mersed in water. 



It will be perceived that all these processes are nothing more 

 than preparatory measures for the operation which is to succeed, 



viz., that of TINNING. 



For this purpose an iron pot is nearly filled with a mixture of 

 block and grain tin, in a melted state ; and a quantity of tallow 

 or grease, sufficient, when melted, to cover the fluid metal to 

 the thickness of four inches, is put to it. However, as some 

 gentlemen may not be acquainted with the difference between 

 block and (jrain tin, it may be remarked, before we proceed, that 

 tlie metal known in commerce by the name of block tin, is pre- 

 pared either from the mineral called tin-stone, or the one 

 known in Cornwall by the name of tin-pyrites, whilst the article 



Vol. VIII. L 



