78 abstracts: technology 



TECHNOLOGY— .So/»e kadless fritted glazes. E. T. Montgomery. 

 Bureau of Standards Technologic Paper. (In press.) 



In the manufacture of American whiteware, china and porcelain and 

 of English bone-china, a glaze composed of borosilicates of the alkalies, 

 lime, lead and alumina maturing at a relatively low temperature (about 

 cone 3, approximately 1100°C) is applied to a body previously fired to 

 the desired maturing point fof the given body, approaching vitrification 

 more or less closely. It is essential in this process that the maturing point 

 of the glaze be considerably below that of the vitrification temperature 

 of the body in order to avoid, in the glost fire, undue softening of the 

 body and consequent deformation and loss. To accomplish this purpose 

 and at the same time to secure their inherent qualities of long tempera- 

 ture range, brilliancy and low viscosity, such low fusing glasses as boro- 

 silicates containing lead oxide are employed. 



Chiefly on account of the poisonous nature of the lead compounds 

 used in making these glazes, the subject of leadless glazes has aroused 

 the interest and has received the serious attention of both technical 

 ceramists and of manufacturers for many years. The present work was 

 undertaken for the purpose of investigating the merits of the various 

 types of leadless glazes thus far reported, of studying their properties 

 and possibilities, of improving them if possible; and of making a general 

 comparison from a technical standpoint, between lead and leadless- 

 glazes for whiteware and china at a glost heat of Segar cone No. 3 (ap- 

 proximately 1100°C). 



To this end numerous series of glazes were made up, being so planned 

 as to include a number of previously reported leadless glazes of merit, 

 and all methodically arranged in such a way as to fully cover the range 

 of composition which it was believed desirable to study. All of the glazes 

 were tested over six standard underglaze colors of known composition 

 and all of their properties were studied in direct comparison with a stand- 

 ard whiteware or china glaze made with lead, half of each trial being 

 dipped in this standard lead glaze and half in the leadless test glaze. 



The results of this investigation developed many interesting technical 

 points both in regard to leadless glazes in themselves and in comparison 

 with lead glazes. In general, we may say that while lacking some of the 

 valuable characteristics and qualities of lead glazes, leadless glazes have 

 a few distinct advantages of their own. On the other hand, it is the 

 writer's opinion that it would be premature at the present time to say 

 that we can make a leadless glaze for whiteware, china or porcelain 

 which could be substituted for the present lead glaze. E. T. M. 



