78 
KERAMIC STUDIO 
GRAND FEU CERAMICS 
Xin-GRAND FEU COLORS— Colored Glazes-FIamme Glazes— 
Flowing Glazes 
Taxile Doai 
OLORED pastes used on small sur- 
faces give to the decoration a finn- 
ness and a character of soliditj^ 
which are very attractive; but used 
on large surfaces they impart to a 
vase a heavy, marble like appear- 
ance. This defect led to researches 
for the incorporation of color with 
the glaze and gave birth to colored 
glazes. Colored glazes are real 
translucent colored glasses, and the color dissolved in them is, 
as for pastes, derived from metallic oxides. The basis for these 
glazes is the colorless glaze, called white, with which the por- 
celain is covered, and into which are introduced by careful 
grinding and mixing a few hundred parts of coloring oxides. 
If one wishes to obtain the exact value of tone which the 
formulae in these articles are capable of giving, it is necessary 
to use oxides free from all impurities. This purification is the 
duty of technical chemists. The analyses which are necessary 
in order to obtain the best products are minute and delicate 
and, consequent^, slow and expensive. A ceramic artist 
cannot undertake them, as he must give his time to the ab- 
sorbing experiments of his art. He must be, as I am, satisfied 
with materials as he finds them, avoiding for some tones a 
certain harsliness which is caused by too pure materials, but in 
other cases, submitting to the vma voidable result of impurities. 
Cobalt free from nickel gives a fine blue tone both in day- 
light and artificial light. When it contains nickel, it is duller 
in the da5^1ight and black in the artificial light. Notwith- 
standing their purit3^ the Sevres blues are black in artificial 
light, while the old Chinese blue porcelains remain blue in all 
kinds of light, How did these empirics of genius manage to 
do it? 
At Sevres, all materials, before being used, are anah^sed in 
the laboratory- and tried in the fire. This is the secret of the 
fixitj^ and richness of colors used on the various ceramics which 
are made at Sevres. For vny own work I have to be satisfied 
with frittings and grindings made with the greatest care, and 
with the greatest possible precision in the conduct of the firing. 
And it is a great deal to succeed in doing that with modest 
resources. 
I wish to call the attention of artists to cases in which they 
will be obliged to modify the formulae given below, which have 
been worked out for two bodies, PN and Lacroix-Ruaud. 
As the addition of a coloring oxide to a glaze changes its fusi- 
bilitj^ and its coefficient of expansion, the mixture must be so 
arranged that it will fire at the same time as the bodj^ without 
crazing, and this can be done only by careful experimenting. 
But whether these formulae are used as I give them, or modified, 
it is important to maintain the degree of plasticity which makes 
the glaze adhere to the body. For this, only a small part of 
the elements should be fritted, and the rest should be added 
bj' simple mixture. The intensity of the color is based, not 
only on the quantity of coloring matter, but also on the pro- 
portion of chalk which it contains, the latter varying more or 
less according to the fusibility given to the glaze by the oxide. 
The fritting of colored glazes, carmot be done in the kiln, 
as was the case with colored pastes, because it must be watched, 
and the fusion stopped or continued, according to circumstan- 
ces. Frits are made in a special kihi. 
This kiln is a bla.st kibi (Fig. A) , comnmnicating with the 
chimney of the regular kiln, so as to get the advantage of its 
mtense draft. The kiln is vertical and cylindrical, entirely 
constructed with fire bricks D and contains a fire clay cylinder 
E open at both ends. The upper part is closed with a fire clay 
plaque F with iron bands and a handle to allow of easy Hfting. 
The lower part rests on square iron bars, about l^ inch apart, 
to give free passage to ashes and air. These bars rest them- 
selves on two cross bars fixed in the wall K. The bars of the 
grate can easily be removed to clean the kiln. (Fig. B). The 
ash receiver L, formed bj^ the space below the bars, is wide 
open in front. The fuel is coke which is placed around the 
fire clay crucible O. The top of the kiln communicates with 
the chimney through an oblique opening M made through the 
thickness of the wall. It is easy to watch the fusion of glazes 
by lifting up the cover P of the crucible with flat pincers. 
The number and size of crucibles detennine the size of the 
kiln. The one v>'hich I use is l8 inches high by lO inches 
inside diameter. I use crucibles No. 20 which are 14 inches 
high and 6h wide and make it possible to melt 20 pounds of 
material. The crucible is placed on a fire clay plaque which 
holds it in the center of the fire mouth. This kiln is very 
economical.* 
All the following preparations for colored glazes should be 
thoroughly mixed.: 
Blue: 
Ouartzj' sand of Nemours 
Dry claj'ey kaolin 
Ordinary washed chalk 
Grand feu blue frit, as below 
Frit : Dry and pure cobalt oxide 
Feldspar in flour 
Brown: 
Sand 
Drv clayey kaolin 
Chalk 
strictly 
oxidising. 
.30,5 
20 
19 
Scale brown grand feu frit, as below 33 
oxidising 
*In thi.s country, where oil is a cheap fuel, the little test furnace made 
by H. J. Caulkius & Co., of Detroit, Midi., mil be found very useful and 
economical for crucible work. It can either be used for frittiiig, or by the 
insertion of a small muffle, can be transformed into a small kiln for tests 
and experiments 011 ixircelain. The gas furnaces of the Buffalo Dental 
]Mfg. Co are also suitable for fritting. 
