80 Prof. Hausmann on the Composition of the Ancient 
yellowish colour, are seen ; from which, it may be inferred that 
the vases have not been manufactured of black clay, but that 
some black heterogeneous matter has been added to the mass. 
The smooth surface of these vases has a certain lustre, similar to 
the black varnish of painted vases. 
At first sight, it might be thought that the black colour of 
the mass had been produced by oxide of manganese^ in the same 
manner as in some of our earthen- ware manufacture, first made 
by Wedgwood ; but this opinion is confuted by experiments 
made, with a view to determine its nature. 
The mass of these vessels has a distant resemblance to the fa- 
mous Ipswich crucibles, which are formed of a mixture of clay 
and graphite , and but slightly baked. The graphite, however, 
gives the clay an iron-colour, and the surface of the vessel a me- 
tallic lustre ; whereas, on the contrary, the external colour of 
those antique vases passes into pitchy, and the lustre is like that 
of varnish. 
It is well known, that a black colour may be given to clay by 
means of charcoal vapours. Some sorts of earthen-ware receive 
a black colour from the vapours of mineral coal ; and charcoal 
makers blacken their smoking pipes, by putting them into 
the pile. But that their black colour has not been given to 
these vases in a similar way, may be inferred from this, that 
they have been baked in a very small fire, and that the black 
colour is not equally diffused through the w T hole mass. 
With the view of finding out their true nature, I made some 
experiments, in which I observed the following circumstances : 
1. In the flame of a blowpipe, the black colour of the mass is 
soon destroyed. The mass of vases assumes a reddish-yellow 
colour, which, in a stronger heat, passes into greyish-black, 
which is probably effected by the reduction of the particles of 
oxide of iron. Fusion then follows, by which a greenish or 
blackish glass is produced. % With borax, the black particles 
of the mass afford a yellowish-green colour, which, however, on 
cooling, nearly disappears, — a phenomenon which may be ob- 
served, if any substance contain the smallest quantity of oxide 
of iron. No vestige of a violet-colour, indicating the presence 
of oxide of manganese, could be observed. S. If a little of the 
black mass, reduced to powder, be added to nitre in a platina 
