VOL. LIX.J PHILOSOPHICAL TRANSACTIONS. GQS 



must be quite dry, clean, and cold, in order to give it the figure of the convex 

 tool. In case it lias not spread out so as to cover the whole surface of the polishr 

 ing tool, warm the pitch by holding it before the fire, and press it on the convex 

 tool, as before, till it has entirely covered the surface of the polishing tool; then 

 plunge it into cold water, till the brass is quite cold. 



To know if the pitch is hard enough, press the edge of the nail of your 

 thumb on it, and if it receives an impression, the pitch is not hard enough. 



Then proceed to prepare this polishing tool, for the last polish of the glass, 

 by grinding this polishing tool on the convex tool with pretty coarse emery, and 

 a small quantity of water, in the common way that tools are ground one on an- 

 other; but this must be done only for a short time, and the polishing tool must 

 have no other pressure than its own weight, for fear of some of the emery stick- 

 ing in the pitch, and you must never allow the emery to grow dry; when you 

 have ground the pitch so as to be all over of the same colour, you then wash the 

 pitch from all the emery with a brush and clean water; after this take a bottle 

 of water, and holding the pitch tool in a sloping position, pour water out of the 

 bottle so as to fall on every part of its surface. 



Then place the polishing tool in a horizontal position, and put on it some 

 putty, washed from all its gritty particles, but it need not be the finest washing, 

 and put a good deal of water on the polishing tool, mixing the putty and it to- 

 gether, and polish the glass on this pitch polisher in the common manner of 

 polishing glasses. 



After having polished the glass about 10 minutes, again grind the polisher on 

 the convex tool with emery, as before, for fear the pitch has, by working, lost 

 any of its proper figure; and the oftener you do this, the truer will be the figure 

 of the glass; and in this manner you proceed till the glass is quite polished. 



Then take the glass off^ its handle, by holding it before the fire, till it is so 

 warm that you can slide the handle off the glass; and while the glass is warm, 

 take off as much of the pitch as you can with the sharp edge of a knife; then 

 lay the glass down to cool, and when quite cold drop some spirits of wine on it; 

 and this with a cloth, will wipe off the rest of the pitch. 



Then examine the centre of the surfaces of the glass; and if it lies to one 

 side of the centre of the glass, mark that place with a spot of ink, and then 

 put on the handle as before, on the side that is now polished, with its centre 

 over the spot of ink, and grind the glass as before, till the circular remaining 

 part of the glass to be ground is as much distant from the centre of the glass on 

 the other side from tiie spot, as the spot was from the centre of the glass; then 

 by heat return the handle to the centre of the glass, and proceed to grind and 

 polish this side of the glass as before. 



