54 
KERAMIC STUDIO 
aluminum, or by increasing its penetrating power by the 
addition of nickel. 
Chrome is the basis of greens, from light green or celadon 
to the dark malachite green. It can be modified by the addi- 
tion of cobalt and aluminum. Combined with other materials 
it gives a wide series of tones. Thus pink is a combination of 
chrome, zinc and aluminum. Combined with lead, it gives 
yellow; with iron, brown. 
Nickel which has a great affinity for cobalt, is almost 
always found close to it in nature. The brown palette comes 
from this metal which possesses the greatest power for pene- 
trating vitrified matter. 
Copper, a marvelous metal, runs, dvuing firing, through the 
whole ganmt of the most opposite tones. According to the 
atmosphere in which it is developed, it gives black, green, 
turquoise blue and scarlet red. It becomes metal, flows, is 
translucent or opaque, according to the materials with which 
it is mixed. And if it is the nrost difficult metal to control, it is 
also the good fairj? of ceramists because of the charm of its 
unexpected eft'ects. 
Iron, so common in nature, is used in all its forms, col- 
cothar, battitures, bol d' Armenie, Terre de Sienne, yellow or 
red ochre, ferruginous silicate of Thiviers, etc. It is the basis 
for browns, reds and violets. It is both a source of trouble and 
a providence to ceramists, troublesome because it gets in- 
crusted in the white, and providential because of the variety 
of tones which it gives to other metals. 
Uranium is, like copper, among the erratic metals. It 
gives both yellows and blacks, going from citron yellow to 
yellow brown, and from grey to deep black. 
Manganese, either common or ferruginous, and pure 
metallic manganese may enter into coloring combinations. 
They produce brownish black, violet, reddish brown and j^ellow. 
In most cases this coloring gives metallic reflections. 
Iridium gives greyish blacks of a great delicacj- and of great 
charm. 
Platinum gives to the flux of the body and the vitreous 
glaze only a lead grej^ color half-way between the color of silver 
and that of tin, but it is the only metal which gives fixed tones 
which vary neither in oxidising nor reducing fires. 
The two precious metals, gold (t030°-C) and silver (770°-C) , 
which melt at comparatively low temperatures, disappear in 
porcelain firing. 
The metals which I have just mentioned are those which 
have alread5^ been used bj^ ceramists as coloring agents, but 
their combinations are far from being exhausted. And other 
metals are just beginning to be experimented on. Molybdeniun, 
ruthenium, titanium, vanadium which have a great future, wiU 
tempt bold experimenters. 
Metallic oxides and their compounds act differentlj' 
according to the nature of the atmosphere in the kiln. Thej^ 
must be studied for the kind of firing in which they will be 
used. So uranium gives black in reducing, yellow in oxidising. 
Copper, green in oxidising, is red in reducing. From this fact 
it will be seen that the scientific regulation of the kiln atmos- 
pheres has doubled the coloring resources. But certain metals, 
zinc for instance, are volatilized and completely disappear in a 
reducing atmosphere. 
Ceramists who use only one or two metals have not anj' 
mistakes to fear, but those who want a varied palette must 
carefuUj'^ label their colors, in order to avoid disappointments 
such as I had one daj' when I accidentally used a celadon of 
copper glaze instead of a celadon of iron. The vase, when 
passing through a reducing atmosphere, became of a blackish 
red which concealed all the decoration. This was due to the 
fact that oxidised or desoxidised gases, according to the atmos- 
phere, favor by afifinity the development of one of the metals 
which enter into the composition. 
Coloring oxides may be combined either with the paste or 
with the glaze. They give different effects with these different 
combinations. 
When the color is mixed with the paste, it forms with it an 
opaque mass which remains fixed, is not displaced, and allows 
the superimposition of other pastes. This constitutes what is 
called colored pastes. 
If the same coloring matter is added to the glaze, the 
latter becomes more fusible and acquires a tendency to flow, 
thus making it impossible to superimpose a decoration. This 
combination gives the colored glazes. 
These two processes complete each other, as the colored 
glaze may safely flow over a pa.ste decoration which remains 
fixed. 
Colored ])astes are not of a complex preparation. It is 
sufficient to add to the white paste a few granunes of coloring 
oxide and to mix with water. 
The greens which I use in the shape of paste are prepared 
as follows by simple grinding: 
Light celadon. Dark celadon. 
Chrome oxide 2 Chrome oxide 5 
PN white paste 98 PN white paste 95 
100 100 
One may go up to 10% chrome. Although these two 
colors stand both firings, the light celadon is finer in oxidising, 
and the dark celadon in reducing. 
If only a small quantity of paste is needed, the mixture 
can be made on a rough glass with a muUer; and with water. 
For a quantity of more than one pound, a hand mill should be 
used. Chrome pastes have a remarkable distinction and 
delicacy, but have not a great power of infiltration through 
other pastes. In order to give more delicacy to their combi- 
nations, one may add to them from 3 to 5 grammes zinc oxide. 
The blue pastes which I use are made as follows : 
Light blue — 
Mediiim- blue- 
Very dark blue — 
Cobalt oxide 
PN white paste 
Cobalt oxide 
PN white paste 
Cobalt oxide 
PN white paste 
4-00 
96,00 
I 
10,00 
90,00 
Cobalt has a very great coloring power, bvit must be 
ridden of the nickel which it contains and for which it has a 
great affinity. If on a cobaltiferous paste another colored 
paste, or simply a white paste, is laid, the latter will be pene- 
trated by the cobalt oxide. This infiltration through a white 
paste laid over a cobaltiferous paste, has given birth to the 
process of decoration called pate sur pate or applied pastes. 
^ Colored pastes must have the following qualities: such a 
degree of plasticity that they can securely be applied to the 
piece and make a whole with it; coefficient of expansion 
identical to that of the porcelain itself, so that creasing, blisters 
and cracks will be avoided. Besides they must be mixed as 
thoroughl}^ as possible either by grinding or fritting, so that 
thej^ will give uniform tones without spots or shading. 
The mixture by grinding is \ery simple. It is done with a 
muller and a palette knife. 
The mixture by fritting is more complex and requires 
practice. A jrit is the product of the calcination or fusion of 
