646 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
It was the Royal Manufactory at Copenhagen which, in 1885, first 
demonstrated the advantage obtained by the decoration of porcelain 
at a high temperature (1,400°). 
The factory at Sevres followed it in this process and with very 
great success, for it had possessed for a long time the knowledge of 
the decoration with colors at high temperatures, which had been 
investigated there long before it had been carried out at Copenhagen. 
Sévres possessed a range of tones much more vigorous than those in 
use at Copenhagen, as may be observed by comparing the products 
of the two establishments. 
I must now take up the subject of stoneware (grés), to which 
Brogniart has added the name of cérame to distinguish it from the 
natural grés (sandstone) which is that abundant rock, certain hard 
varieties of which are utilized in making mill stones and paving 
blocks. 
I may first mention the fact that there are four classes of ceramic 
_ products, earthenware, faience, stoneware, and porcelain. The first 
two are made of unvitrified paste and are consequently porous. 
The other two are of vitrified paste (after baking of course) and 
are impermeable. 
Porcelain is the most beautiful of all these ceramic products, but 
its very high price largely limits its use. However, as vitrified clay 
articles are much superior to the unvitrified, in the last twenty years 
stoneware has been accorded a most important position. 
At the same time that stoneware was adopted into the art a special 
decoration was applied to it, consisting of covered colors obtained 
by the mixture of a coloring agent with a colorless covering. 
Stoneware is baked at 1,250° at most, at a temperature consequently 
much lower than porcelain. No faith should be given to the asser- 
tions of certain ceramists who pretend to bake their stoneware above 
the temperature I have just indicated, some of whom talk tempera- 
tures as high as 1,800° to 2,000°. 
Others do not hesitate to claim that the manufacture and decora- 
tion of stoneware are much more difficult than with porcelain. I 
hear this absurdity continually repeated, but I am sure that experi- 
ence would lead them to a change of mind in this regard. 
In considering the question of stoneware, the idea came up of 
resuscitating an old color discovered in 1792 by the German chemist 
Klaproth. This is the color based on titanic acid. Titanic acid is 
met with abundantly in nature, associated to the extent of 2 or 
3 per cent with oxide of iron. It appears in the form of a red 
crystalline mineral called rutile. One of the most remarkable 
properties of rutile is that it gives a mat finish to covering layers in 
which it is incorporated. These mat finishes have been declared 
the supreme perfection in ceramic decoration, though no one will 
