568 NEW YOKK STATE MUSEUM 



Without giving tlie composition of the clays wliicli Seger ex- 

 perimented on, in this connection it may be interesting to give some 

 of his conclusions. 



The first group' includes the porcelain clays, and in these the 

 ferric oxid may at times exceed Ifo without influencing the color. 

 In this connection it is considered that the presence of a large 

 amount of alumina has the same effect as lime, in destroying the 

 red color of the iron. Evidence of this fact is afforded by Seger's 

 experiments on clays included in the second group. 



In the second group are included clays which burn white at low 

 temperatures, with an occasional pink tint, but at higher tempera- 

 tures show more or less yellowish or brownish color, but never a red, 

 assuming a greenish color at the highest temperatures due to the 

 reduction of the iron to a ferrous condition. The alumina in clays 

 of this group is generally 20 fo-SOfo and even more, while the per- 

 centage of ferric oxid may in some cases approach that of the brick 

 clays, but it generally ranges between 1^ and 5^. It is an interesting 

 fact that a mixture of red burning clays of the third group and 

 kaolin does not give a pale red product on burning, but. instead a 

 yellow one, which Seger believes is due to the excess of alumina. 



This group includes many fire clays, semi-fire clays, stoneware 

 clays. Five examples are given by Seger to illustrate this effect of 

 the alumina in destroying the red color, of the ferric oxid. Their 

 color when burned, as well as the ratio' of ferric oxid tO' alumina, is 

 given below. 



r!n1 or wh Pn hnrnPfl White to Lifflit Yellow to Yellow Vpllnw 



<^olor wnen Durnea yei. white yellow light brown brown iieiiow 



Ratio of ' ferric 



oxid to alumina 1:13.2 1:7 1:5.4 1:7.2 1:6.3 



The exact temperature at which these were burned is not stated 

 but it was the same in each case. 



This group somewhat resembles the fourth group in respect to the 

 colors produced, but differs from it in fusibility, becoming porce- 

 lain-like at high temperatures, and not green, but brown or gray in 

 color. The percentage of alumina, it will be seen, far exceeds the 

 iron. The color seems to be lighter the greater this excess. 



