THE YOUNG 
sometimes applied to delicate models, I 
which will not bear the use of mallet and 
chisel. This is practiced by pouring 
melted wax over the model, to form an 
inner mould, and then backing, as usual, 
with plaster. This wax mould can be 
pulled away from the cast, with a little 
warming, without danger to the finest 
work. 
It is by one or other of these processes 
that the clay model has always to be 
transformed into a plaster cast. Biit if it 
is required to multiply copies of such 
casts, or of other suitable objects, other 
means than waste-moulding will have to 
be resorted to. This must be done either 
by an elastic mould or by a piece mould. 
Mastic Moulds. — First, as to the elastic 
mould, which is recommended—by its 
simplicity, and the ease with which it can 
be made — for those purposes to which it 
is suited. Its value may readily be per- 
ceived. Fig. 6 may be supposed to repre- 
sent one quarry of a diaper, which has 
been modelled, and of which a number 
will be required. Fig. 7 shows the same 
in section. 
It is plain that no mould formed in a 
single piece from any rigid material could 
leave this panel without breakage; but 
we get over the difficulty if we make our 
mould of some substance so yielding as to 
allow it to be drawn over the projecting 
points seen in the section, and so elastic 
as, when drawn off, to recover its former 
shape. From such a mould we can take 
as many casts, in moderation, as we may 
require. 
Various substances have been used for 
making such moulds, but that most ap- 
proved by the best moulders is gelatine. 
Having first made a single cast by the 
waste-moulding process, take best sheet 
gelatine 1 lb., beeswax i oz., water I of a 
pint. Boil them in a glue-pot till they 
lorm a thick syrup; rub a little oil (or 
what is better, hog's lard) over your cast, 
and then pour on the mixture. It should 
be used warm, but not boiling. The best 
and purest gelatine, at about fifty cents 
per pound, should be used. Some use 
glue, or cheap gelatine ; but these cannot 
be recommended. When the mould 
comes to be filled, the plaster grows 
SCIENTIST. 145 
warm in setting, and the heat thus gener- 
ated is apt to melt an inferior mould. 
Piece Moulding.— By this method ob- 
jects in the round, objects in relief if they 
are large, and indeed most objects f L-om 
which a casting mould is required, are 
moulded. It is by this method that tlie 
cheap plaster images, and almost all the 
plaster casts sold in the shops, are pro- 
duced. 
[Note.— The cuts, 4. 5, 6 and 7, referred to in the 
text, will appear in next month's article OH 
" Casting in Plaster of Paris."— Ed.] 
(To be continued. i 
t-O-* 
Overglaze Painting on Porcelain- 
BY AURELIO DE VEGA. 
r^r^lNTIQUITY of Pottery Ornamen- 
awa^^ tation. — The decoration of arti- 
^^\J cles made of clay is one of the 
wM^N^ evidences of that longing for 
ornament of some kind or other, 
which seems to be inherent in man, and 
we accordingly find that the art of pro- 
ducing on clayware, in such a manner 
that the result should be permanent, de- 
vices of a color different from that of the 
ware, is prehistoric ; the earliest records 
on this point being in fact induced by the 
circumstance that excellence had already 
been achieved in the art. 
2. Super iority of Porcelain to Earthen - 
loare.— For our purpose clay goods may 
be divided broadly into two classes- 
opaque and translucent : the former com- 
prising earthenware, majolica, and the 
like; the latter, porcelain or china. Ti e 
worth of earthenware may vary between 
that of the commonest clay crock and the 
finest i)iece of stoneware, or majolica ; but 
the value of porcelain, which is of a su- 
perior basis, of a more delicate texture, 
and more expensive to ]:>roduce, vn.ries 
within comparatively small limits. That 
is, of course, at the time of production, 
and with due regard to the amount of 
work entailed in forming the object inxo 
which it is to be made. The specimens 
which realize such extraordinary prices 
among collectors have an enhanced or a 
spurious value from being ancient or typ- 
ical, or from the mere determination of a 
person to become the purchaser. My re- 
marlcs upon decoration are made ijri- 
marily with reference to i~)orcelain ; not 
simi)ly because it is the finer and intrin- 
sically more valuable material, but also, 
and princi]:»ally, because upon it work 
more excellent in appearance can be pro- 
duced. At the same time it will be under- 
stood that they apply also to earthen- 
ware. 
