Witt: Pottery in the Vicinity of Manila 



61 



ware are almost above criticism. However, most of the Philip- 

 pine ceramic products that I have seen lack stren^h. This 

 is true of bricks as well as of most pots and jars, and it prevents 

 the manufacture of a really durable product. In the kilns de- 

 scribed a few of the articles are burned very well. However, 

 those nearest the fire doors are usually overburned and fuzed 

 out of shape, and many more are not sufficiently burned to 

 develop the maximum strength of the material. The ware manu- 

 factured without the use of a kiln is all underburned. This 

 was verified by experiments. 



Some of the mixture in daily use at one of the potteries 

 was brought to the laboratory, and several experimental 

 bricks were molded and dried. These were divided into two 

 lots: the first was taken back to the pottery and burned with 

 some ware in the regular way — not in a kiln. A pyrometer 

 was installed, and readings were taken every five minutes during 

 the operation. The other set was burned in an experimental 

 kiln at the Bureau of Science. The temperatures in the latter 

 were determined by Seger cones, because they were too high 

 for the thermocouple. 



Table I. — Temperature record of burning in an experimental kiln and 

 in a pile of straw at pottery. 



At pottery. 



! !| 



rp- Temper- 

 ^'""'- ature. 



At pottcrj-. 



In experimental kiln. 



Time. 

 a. Tit. 



Temper- 

 ature. 



Time. 



1 

 Approxi- 

 mate tem- 

 perature, 

 indicated 

 by cones. 



a.m. 



°C. 



1.45 



30 



2.40 



355 



4.00 



«30 



1.50 

 1.55 



MO i 



250 1 



2.45 

 2.50 



290 ' 

 240 



p.m. 

 1.00 





970 



2.00 



515 •' 



3.00 



200 



1.20 



1,010 



2.05 



675 ■ 



3.05 



160 ; 



1.45 



1,050 



2.10 



745 !; 



3.10 



130 ' 



2.05 



1,090 



2.15 



755 ' 



3.15 



110 , 



2.25 



1,150 



2.20 



725 ,; 



3.20 



70 



3.25 



1,190 



2.25 



665 : 



3.35 



60 





1 



2.30 



555 { 



3.30 



50 





1 



2.35 







450 









'"" . " " 1 









"" '" 1 



" Initial temperature. 



The temperature-time curves were plotted and are shown in 

 fig. 1, where the contrast in burning operations is readily seen. 

 At the pottery the burning was completed in one hour and thirty- 

 five minutes. The temperature rose to the maximum point, or 

 over 700°, in thirty minutes, and the first stage of the cooling 



