132 THE BOOK OF THE LANTERN. 



or two, during which time it can be conveniently stirred 

 once or twice (by red light only, of course). If the cover 

 of the jar be really light tight, this melting operation can 

 go on in daylight, and at the same time the glass to be 

 coated can be cleaned. Polish each glass with a little 

 whiting and water, and when dry rub the side to be 

 coated with a leather damped with spirits of wine. This 

 will counteract any repellant action when the emulsion is 

 applied to the glass surface. When all the glasses have 

 been so treated, wrap them in packets of two dozen each, 

 in clean paper, prepared side upwards, and put them on 

 the kitchen hob to warm through. (This latter precaution 

 is only necessary in cold weather.) The emulsion must 

 now be filtered. 



The best form of filter is a lamp chimney with a flange 

 on its lower orifice, over which a piece of damp wash- 

 leather (which has been washed in soda and rinsed in 

 many changes of water) can be tied. When all is ready 

 for commencing to coat, this filter is held over the mouth 

 of the jug (both should be rinsed out with warm water 

 the instant before), and the emulsion is poured steadily into 

 its upper opening. In a minute it will run through the 

 leather into the jug below, and will be quicker in its move- 

 ment if a pressure of air is kept upon it, by applying the 

 lips to the upper end of the glass. Now comes the coating 

 difficulty. 



Let the operator seat himself at his table so that the 

 slate or glass slab is between him and the red light. 

 Place the glass rod in the jug of emulsion, and when in 

 the act of pouring keep the rod back with the thumb of 

 the same hand that is holding the jug. Take the topmost 



