VOL XXXV.] I'MILUSOPHICAL TRANSACTIONS. 307 



receive the immediate action of the hammer, otherwise they will not extend 

 equally : the second is to steep them in clay or fuller's earth, tempered with 

 water, before heating them, to prevent their soldering with each other. 



He then closes this part of the operation with remarking, that whichever of 

 these methods is pitched on, whether the old one, of which he has learnt the 

 secret, or any of the new, which he has here shown, it is absolutely necessary, 

 after the plates are sufficiently scaled, to scour them with sand ; and when no 

 more black spots remain on their surface, to throw them into water, to prevent 

 their rusting again, and leave them in it till the instant they are to be tinned, 

 or blanched, as it is called. 



This he observes is the very object of the whole art, and is kept as much 

 a secret by the blancher, as the acid eroding menstruum is by the scaler : but 

 the manner of doing it is thus. They flux the tin in a large iron crucible, 

 which has the figure of a pyramid frustum with four faces, of which the two 

 opposite ones are less than the two others. This crucible they heat only from 

 below, its upper border being luted in the furnace quite round. The depth of 

 the crucible always exceeds the length of the plates to be tinned, which are 

 always put in downright, and the tin ought to swim over them. 



For this purpose, artificers of different trades prepare the plates in different 

 manners, which are all exceptionable: but the Germans he perceived made use 

 of no preparation whatever, except putting the scoured plates into clean water, 

 as just remarked; but when the tin is melted in the crucible, they cover it with 

 a layer of a sort of suet, an inch or two thick, through which the plate must 

 pass before it comes to the tin : the first use of which is to keep the tin from 

 burning, and if any part should take fire, as the suet will soon moisten it, to 

 reduce it to its natural state again. This suet is a composition, as the blanchers 

 say, and is of a black colour, which the author thought might be given it with 

 soot or the smoke of a chimney, only to spread a mystery over their work; but 

 he found it true so far, that common unprepared suet was not sufficient : for 

 after several attempts, there was always something wanting to render the success 

 of the operation certain. The whole secret then of blanching lies entirely in 

 the preparation of this suet : and this he at last discovered to consist only in 

 first frying and burning it ; which not only gives it the colour, but puts 

 it into a condition to give the iron a disposition to be tinned, which it does 

 surprisingly. 



The tin itself ought to have a certain degree of heat ; for if it be not hot 

 enough, it will not stick to the iron; if too hot, it will cover it with too thin 

 a coat, and the plates will have several colours, as a mixture of red, blue, and 

 yellow, and the whole appear of a bad yellow cast. To prevent this, by 



