649 
covering layer. By a large proportion I mean from 20 to 30 per cent. 
The covering should be applied to the piece in a very thin layer, 
however, 2 millimeters at most. 
The reduction should be an energetic one, and in this connection 
I have observed that this can be controlled by the proper regulation 
of the draft damper. The constructors of kilns have gotten into the 
bad habit of placing this directly over the grates, and I have noticed 
that such a practice is injurious to the proper operation of the kiln, 
while if the regulator is placed at the base of the chimney, which 
surmounts the dome, the draft is perfectly even; it can then be regu- 
lated in such a way that the interior atmosphere may be rendered 
at will either strongly oxidizing or strongly reducing. 
In an oxidizing fire a lead glaze with copper acquires that vivid 
green tone which has always been very popular among primitive 
peoples, and which is still in general usage in the north of Africa— 
for example, in Algeria and Morocco, in spite of constant contact 
with France—in Italy, and in Spain. An alkaline covering (rich in 
potash and soda) acquires a remarkable blue tone (Egyptian blue), 
to which may be given a greenish tinge by the addition of lead. This 
gives a turquoise tone. 
In a reducing fire the green glaze, the blue glaze, or the turquoise 
become red, but the last is alkalino-plumbous and will always give a 
much more beautiful red than one containing only lead. 
With this red I have associated the titanium blue. We have seen 
that rutile, natural titanic acid, gives a yellow or brown-yellow in an 
oxidizing fire. Under the influence of reducing gases, the titanic 
acid passing over into the blue sesquioxide of titanium is an impor- 
tant feature in the decoration of the flamed pottery. This titanium 
blue has the remarkable peculiarity of preserving its blue tone in 
artificial light, instead of appearing brown like the cobalt blues, or 
green like the copper blues. 
When the copper red and the titanium blue are combined on the 
same piece, violet would ordinarily be expected, but each color keeps 
its own shade. Violet can nevertheless be produced as I have ob- 
served in extremely rare cases, an effect due, perhaps, to particular 
conditions of reduction that escaped my attention in the firing. 
Violet tones in the flamed ware can be easily obtained, however, by 
combining the copper red with the blue of cobalt if the latter is not 
added in too great excess. 
Finally, I have obtained some curious modifications of tone by 
combining copper, sesquioxide of titaniumand glucinum. (Isay cop- 
per and not oxide of copper because, according to the theory of Ebell, 
the coverings are colored red, not by the oxide but by the metal 
itself.) I introduce the glucinum in the form of silicate, conse- 
