86 THE YOUNG 
bottom of the basin, and by a quick mo- 
tion, witliout bringing its bowl to the 
surface, the ]>laster is made to boil up. 
Tliis is the proper motion to use. As 
soon as tlie mixture is of an even consist- 
ency, sl^im oft" the impurities and those 
bubbles which in spite of all your care 
will have formed, and throw them away. 
When mixed, the plaster will be of the 
consistency of thick cream. All these op- 
erations, which take some time to de- 
scribe, must be done quickly. No mo- 
ment must be lost wdiilst mixing the plas- 
ter, or you will have it set before you are 
ready to use it. 
Now, witli the spoon, throw the plaster 
all over the face of the model. See tliat it 
goes well into every nook and cranny, or 
you will have an imperfect mould. Be- 
neath undercuttings you can dash plaster 
I'rom the spoon. Have a jxiir of bellows 
at hand, and with them, by ))lowing the 
liquid plaster, you can force it in, and tbe 
air out of, the hollows. See that every 
liair's- breadth of the clay is covered. But 
whilst you are busy doing this, beware 
that you do not with spoon, hand, or oth- 
erwise touch the surface of the soft clay, 
or mischief will ensue. 
Mix more colored plaster, if necessary, 
and go on till you have laid a coating a 
qua r1 er of an inch thick over every ] la rt 
of the model ; but do not trouble to leave 
an even surface: it is belter that there 
should be some lumps and irregularities, 
which will serve to hold this inner mould 
to 1 he outer one. 
Tlie inner mould is now made, and in 
making it you will have had to bestir 
yourself. You nia,y now take breath, and 
pause for five minutes, at the end of which 
time you will i)robably find your mould 
firm enough for the next process. Mix 
some modelling clay and water as thick 
>as cream, and with a small brush (a 
painter's tool) go over the mould. The 
object of this is to cause tlie outer and 
inner moulds to separate readily when re- 
quired to do so. 
The outer mould we have now to make. 
Por this i)urpose coarse plaster is suffi- 
cient. Now and for future operations you 
will use not colored but plain water. But 
because you are using coarse i)laster, do 
not mix it carelessly. It is of much im- 
portance that plaster should always be 
properly mixed; and after each mixing it 
is well to cleanse out the basin, and espe- 
cially when on the more particular parts 
of the work, with fine plaster. With 
coarse |:>laster it is not necessary to be 
quite so particular. 
A layer of coarse plaster having been 
thrown or poured all over the mould, and 
allowed slightly to harden, irons will have 
to be laid on to strengthen it. As plas- 
ter sets and dries it tends to warp, hence 
the necessity for thus strengthening the 
SCIENTIST. 
mould. Persons who are frequently in 
the practice of making waste moulds, 
such as sculptors, keep by them a quan- 
tity of thin iron bars of different lengths, 
and bent in ditTerent ways, to use as occa- 
sion may require. But any pieces or in- 
struments of iron of suitable size thai 
may first come to hand will do. When I 
was a student at South Kensington, 
twenty years ago, instead of the present 
stately buildings, the Art Schools were 
mere temporary sheds attached to an old 
suburban residence, and the kitchen of 
the former mansion formed our casting 
room. Whenever a bas-relief was cast, it 
was noticed that the poker and tongs in- 
variably disappeared — Jiad the gridiron 
and ladle of the old kitchen slill hung in 
their })laces they would inevitably have 
gone into the mould also ! In short, any 
l)ieces of iron which will stretch froiii 
side to side of the mould and prevent 
warping will suffice. More plaster will 
have to be i)oured on in order to imbed 
Ihem, and the outer mould should thus 
be brought to a general thickness of not 
less than three-quarters of an inch. 
After an interval of about half an hour 
the moidd will be found to have thor- 
oughly set, and we may now begin to 
sei)a,rate it from the model. Where the 
]>laster touches upon the board round the 
outsides, there will be no adhesion be- 
tween it and the wood, and the slightest 
effort will oi)en a chink between them. 
Irito this chink water must be poured, 
and the mould gently worked up and 
down with the hand. This will cause the 
water gradually to work its way between 
])laster and clay, softening the latter, aiid 
if the model is iiot in very high relief, and 
there are no considerable undercuttings, 
with a little patience and frequent ]^our- 
ings in of water, the mould will presently 
come off. Still it will probably bring 
some projecting pieces of clay with it, 
which should be picked out with some of 
the wooden modelling tools, ]iot with 
any iron instrument, for fear of injuring 
the mould. But if the ornament should 
be in high relief, and the imdercuttings 
should be considerable, this plan will i]ot 
answer. Instead of it, a string or wire 
should be passed into the before-men- 
tioned chink, between wood and plaster, 
and with it the model, mould and all, cut 
from the board. The string will cut 
through the soft clay with little diffi- 
culty. The mould can" now be laid on its 
back, and the clay dug and pulled out of 
it, wooden tools and fingers being best to 
use. Whilst doing this a little water 
should often be poured between clay and 
plaster, as it will much expedite their 
sei^aration. 
The clay being by one means or the 
other removed, the mould must be thor- 
oughly washed with soap and water. A 
