April 6, 191 6] 



NATURE 



125 



levitrified glass, or a glass opacified by the addi- 

 ion of clay ; afterwards Bottger, a pupil of 

 vValther von Tschirnhaus, who had had a great 

 leal of experience in the manufacture of crucibles 

 or his alchemical work, made a vitreous body 

 vhich had some of the qualities of porcelain, but 

 m objectionable colour. The ware was very vitreous 

 ind no glaze was used ; Bottger seems to have 

 ried to get the bright glossy surface by polishing 

 he body. Bottger then found a deposit of white clay 

 it Aue, near Schneeburg, and, by using that in 

 jlace of the crucible clay, he was able to produce 

 air imitations of the body of Chinese porcelain, 

 'md a works was started near Meissen in which 

 ixtreme precautions were taken to preserve the 

 ecret. This porcelain was the type now known 

 |:s hard or felspathic porcelain. A generalised hard 

 'x)rcelain body has the composition :— 



Ml 



Clay 



Felspar 



Ouartz 



50 



25 



e discovery of china clay at St. Yrieix, in 

 nee, enabled the French potters to take up the 

 nanufacture of this same type of porcelain, but 

 in Fr'ance a totally different type of porcelain was 

 in use. It was called soft porcelain. The composi- 

 •ion of soft porcelain can be generalised into the 

 jecipe : — 



Calcareous clay ' •■• ^o 



Glassy frit ... ... ... ... 30 



Quartz 40 



Soft porcelain lent itself peculiarly well to the 

 production of beautiful pottery, but the cost of 

 I nanufacture was too great to enable it to com- 

 pete siiccessfully with the bone china and hard 

 lorcelain; as a result, the soft porcelain industry 

 |S virtually dead. Artificial teeth, however, are 

 nade from a variety of soft porcelain. 

 ^ Cookworthy, of Plymouth, discovered that the 

 ;:ornish stone and china clay of Cornwall could 

 )e employed for making a porcelain bodv, an--' 

 jvorks were started at Plymouth. The English 

 jiard porcelain, while preserving a special charac- 

 "" of its own, belonged to the same general type 

 ■le German and Chinese. The manufacture of 

 nis hard porcelain in England does not appear 

 ;0 have been very successful, and was soon aban- 

 iloned. A third type of porcelain developed in 

 f^ngland, the English porcelain, or bone china. 

 I he body of this can be generalised in the 

 ecipe : — 



Bone ash ... -o 



Clay :: ::: ;:; ^° 



Cornish stone 2" 



' ^ e have considered only the bodv of the vari- 



porcelains. The composition and character 



■t the various glazes are of equal importance. 



shortly, hard porcelain, which matures at the 



laze temperature— which is verv high— has a 



A \A ""^ ^^^ "^^^^r^ of felspar; soft porcelain 

 ad a lead glaze which matured at a comparatively 

 3w temperature. 



TThe manufacture of potterv is very largelv de- 

 pendent upon a multitude of conditions, each one 

 I NO. 2423, VOL. 97] 



of which might appear to be of little intrinsic 

 importance. Successful potting involves close 

 attention to detail, and this probably more than 

 in any other industry. 



There is a marked difference in the behaviour 

 of these three types of ware in the firing. In all 

 types of pottery there is a range of temperature 

 or margin of safety outside which the fireman 

 must not go. If the temperature be above these 

 limits the ware is liable to be spoiled ; and if 

 below, the ware is insufficiently fired. With hard 

 porcelain there is a particularly wide margin of 

 safety ; with soft porcelain the margin of safety 

 is so narrow and the resulting losses so great that 

 the manufacture had to be abandoned as com- 

 mercially impracticable. With English bone 

 china, too, there is a comparatively narrow 

 margin of safety, which is necessarily attended 

 by proportionate difldculties. 



Hard porcelain, unlike soft porcelain and bone 

 china, is first baked at a comparatively low tem- 

 perature, and the glaze and body are subse- 

 quently fired together at the higher temperature. 

 The preliminary baking is not a critical opera- 

 tion, and it can virtually be done by the waste 

 heat of ovens firing at the higher temperature. 

 \\'ith soft porcelain and bone china two critical 

 firings are needed; with hard porcelain there is 

 one. The first or biscuit fire with soft porcelain 

 and bone china is much the hottjer; the second 

 or glost fire is not so hot. 



Hard or felspathic porcelain and bone china 

 virtually command the world's porcelain market. 

 Both forms are porcelain, and both are collo- 

 quially called china, although the latter term is 

 more commonly applied to the English porcelain 

 as distinct from the Continental. It appears that 

 in quality — presumably aesthetic — British porce- 

 lain reigns supreme; but in certain special lines — 

 chemical, electrical, and possibly hotel ware 

 — the Continental porcelain has important 

 advantages which render it advisable to start 

 seriously making it in England. Just as 

 the manufacture of the British type of por- 

 celain has not been particularlv successful 

 outside this country, so the manufacture of Con- 

 tinental porcelain has not been successful here. 

 The two types have developed on different lines, 

 and certain radical differences obtain, so that 

 certain conditions necessary for success in the 

 one lead to failure in the other. The cessation of 

 German supplies of chemical ware has led manu- 

 facturers to make fairly good imitations of hard 

 porcelain by modifying parian, insulator, and 

 mortar bodies, but these temporary imitations are 

 not so satisfactory as the true hard porcelain. 

 The problem must be solved bv our taking up the 

 manufacture of true hard porcelain, and "not frit- 

 tering away valuable time on imitations which 

 past experience has proved to be less suitable for 

 the work. The manufacture should offer no in- 

 superable difficulties to our men once their skill is 

 deflected and adapted to suit the special conditions 

 required for the new type of ware. The subject 

 wants tackling boldly and confidentlv on a large 

 scale with British raw materials. If much raw 



