THE YOUNG 
that the result of boiling up, when there 
has been too much oil mixed with the 
paint, is that rough, jagged, or broken- 
blistery appearance, which is similar to 
that presented when a glaze has been sub- 
jected to a greater heat than it was made 
to bear, and which may often be seen on 
common goods. The boiling oil bubbles 
and raises a thin film of paint. The paint 
subsides to the edge of the bubble, and 
when the latter bursts there is left a 
rough-edged hole, with but little if any 
paint within its edge, but with too much 
round it. 
33. The Mediums should he kept in bot- 
tles with closely-fitting stoppers, especi- 
ally the spirits, as otherwise these would 
quickly become "fat" by evaporation. 
For general purposes, corks are prefer- 
able to glass stoppers. The plan I have 
found best is, on getting a new bottle of 
turpentine, immediately to decant the 
whole into small bottles. When a large 
bottle is only half full, the oxygen of the 
air in it attacks the turpentine with the 
formation of water and resin. The most 
useful are little drop bottles, like those 
in which homoeopathic medicines are 
usually put up, and which are furnished 
with a little spout. 
PAINTS. 
34. General Composition.— The colors 
used in painting upon ,china or earthen- 
ware are, for the most part, oxides of cer- 
tain metals. In only a few cases are the 
metals in a simple state used, those prin- 
cipally so employed being gold, silver, 
platinum, and copper ; and these are so 
used only when the natural sheen of the 
metals is required, or in bronzes. The 
jnetal oxides having been rendered as 
nearly chemically pure as possible, are 
either singly or two or more in conibina- 
tion, and in the form of a powder, in- 
timately mixed with triturated colorless 
glasses of varying composition, according 
to the nature of the oxide and the degree 
of hardness required in the pigment. 
The mixture, as ready for use, is an im- 
palpable powder.* When this mixture of 
*0n the more particular composition of china 
colors, as affecting their tints in combination, I 
shall have to speak in a future paper, when treat- 
ing of colors arising from mixture. 
SCIENTIST. 359 
colored oxide and colorless glass is, with 
the aid of the mediums which have been 
described, properly applied to the glazed 
ware, and the pa,inted ware gradually 
raised to a certain degree of heat in a 
specially constructed kiln called a muffle, 
the glaze of the ware, which we have seen 
to be a modification of glass, and the 
glass forming x)art of the mixture, both 
soften sufficiently to enable them to coal- 
esce, and in this increased thickness of 
glaze, the coloring matter is, in the large 
majority of cases suspended, and in par- 
ticles so fine as to be separately discerni- 
ble only in thin films under the micro- 
scope. A few colors, however, such as 
the deep transparent blues, and yellows 
from one source, are really, to a certain 
extent, stained glasses, the glass having 
more or less completely dissolved the 
coloring matter. China or enamel colors 
then, from their containing, as an essen- 
tial constituent, a glass or flux of vitrifi- 
able composition, are called vitrifiable 
pigments. 
35. Home Manufacture of Colors.— In 
this connection I may notice a question 
which has not unfrequently been put to 
me, viz., whether an amateur cannot 
make his own pigments. The answer is 
that in general it is quite possible for him 
to do so, but whether it would be a profit- 
able undertaking is quite another matter. 
The conditions essential to the produc- 
tion in all their perfection of some of the 
most beaut iful colors are such as are not 
attainable except with a very large expen- 
diture of money, and in circumstances 
which do not exist in private houses or 
even in ordinary workshops. In such 
cases the requisite expenditure could 
only be profitable with production on an 
extensive scale and where part of the 
necessary ''machinery" is utilizable for 
other purposes besides mere color-mak- 
ing; and the circumstances, which in- 
clude, among other things, the obtain- 
raent, perception, and maintenance to a 
nicety of different degrees of heat in fur- 
naces of special adaptation are not to be 
■found united except in factories devoted 
to the business. 
(b) Flux.— But these are not the only 
considerations. A very great difficulty in 
