known, has the greatest power of promoting the 

 vitrification of the substances with which it is 

 mixed. The flint serves to give a consistency to 

 the lead during the time of its vitrification, arid to 

 hinder it from becoming too fluid, arid rtirining 

 down the sides of the ware, and thereby leaving 

 them unglazed. 



This glazing, made by means of lead, is liable to 

 be attacked by acids, and is supposed to be pro- 

 ductive of deleterious effects, when employed in 

 jars used for pickling, &c. 



The following composition has been recom- 

 mended as a substitute. 



To make this, white glass and soda, in equal 

 portions, must be very finely pulverized, carefully 

 sifted, and well mixed. The mixture is then ex- 

 posed to a strong heat, till it is rendered, very dry. 

 It is afterwards put into vessels which have been 

 already baked; it is then melted, and the varnish 

 is made. It may be applied in the same manner 

 as that in common use. 



The advantage of it is, that it is safe, and can 

 have none of those poisonous effects which arise 

 from the decomposition of the lead varnish. 



A variety of ware has been of late manufactured 

 which the potters call lustre. The glazing is 

 formed with platina, or gold. For the first, the 

 platina is dissolved in the nitro-muriatic acid with 

 heat: by adding muriate of ammonia, a yellow 

 precipitate falls down : wash and dry it, grind this 

 powder with a small portion of enamel, in oil of 

 turpentine, and spread it thinly over the glazed 

 surface of the earthen-ware. The ware is now 

 baked in a kiln with a red heat, and the platina 

 will assume the metallic brilliancy. 



The gold is managed in the same way. 

 Q 4 



