NATURE 



{_Nov. 7, 1878 



art point of view. All that is now being done in pottery 

 manufacture, all that has lately been achieved in the way 

 of progress, has been here illustrated. An examination, 

 even a rapid one, shows at once how far in advance of 

 other countries England and France are. 



Leaving all strictly art questions out of considera- 

 tion, it is instructive to notice how the technical pro- 

 cesses of manufacture impose limits on an artist's scope, 

 and how these scopes have been widened by recent 

 discoveries. It is not intended in this short note to do 

 more than allude to the more important of these, and 

 before doing so it is worth while mentioning that for 

 domestic purposes English earthenware is still un- 

 approached. 



The pdte-sur-pdte decoration, so largely used in 

 England and in France, is a good illustration of how a 

 process in itself confines the artist's power within certain 

 limits. 



The nature of the ornamentation consists in applying 

 by the brush, and modelling with tools, raised decorations 

 of "paste," which is often, for the sake of artistic effect, 

 in high relief. The paste is of much the same composi- 

 tion as the body on which it is applied, and requires a 

 similar temperature to convert it into China, i.e., T,8oo'' 

 C. The colours which can be used for staining this 

 paste must therefore also be capable of being produced at 

 this heat, and the result is an entirely new range of 

 ceramic colours. It is fortunate for the success of this 

 style of decoration that the colours obtained are har- 

 monious, of a subdued tone. They are quite unlike any 

 that can be produced at a lower heat. Apart from the 

 artist's manipulation, which may vary much in delicacy, 

 the general effect of the production is almost wholly the 

 natural result of the process, and is therefore not due 

 entirely to the artist. 



Another and distinct appHcation of raised decoration 

 is very largely represented in the French court. It was 

 first used at Bourg-la-Reine some ten years ago, and is 

 now made in many other localities. It consists of 

 painting in clay on earthenware with pallet and brush in 

 various gradations of relief, somewhat like impasto. The 

 heat for firing is comparatively moderate, and the range 

 of colours that can be employed is very wide. 



The difficulties of painting under glaze are by degrees 

 being overcome, and one manufacturer has, for the first 

 time, produced gilding iinder glaze. The coloured glazes 

 shown are rich and brilliant, and are well worth the par- 

 ticular notice of those who have paid attention to their 

 production. 



The organisation of the Sevres manufactory and the 

 fact that it is under the direction of a chemist of repute 

 lead to expectations of discovery resulting from the 

 research here carried out. And as a fact discoveries of 

 no small value have been made of late years. Besides 

 such discoveries as of compounds yielding new colours, 

 there are some which take rank as new processes. 



For example, the late Francois Richard, an artist on the 

 staff of the manufactory, found that a large proportion 

 of the enamel colours can be made which will bear a tem- 

 perature of 600° C. — a higher temperature than has been 

 hitherto supposed possible. This higher temperature 

 now employed fuses and softens the glaze ; the colours 

 painted on it blend with it so that, on cooling, there is 

 produced that softness and brilliancy hitherto charac- 

 teristic oi pdte-tendre decoration. This process has been 

 named the de7ni-grandfeu. A great benefit arising from 

 this discovery is that many vases damaged in firing, 

 which would formerly have been abandoned, can now be 

 preserved, as the accidents which so often happen in 

 firing can be repaired. Defects in glaze and colour can 

 be concealed, as, during an exposure to this deini-s^rand 

 feu, they are at melting-point, and new glaze, when 

 added, becomes so fused that no line of junction is 

 visible. This process also gets over a difficulty that had 



long been felt in decorating kaolin, or pdte-diir, china, 

 with a pleasing result, as the colours were always crude 

 and harsh, being on the glaze. When a soft effect was 

 required recourse was had to the less durable and more 

 cosWy pdte-tendfe as a body on which to paint. 



A new method for decorating porcelain where gold 

 alone is employed has been invented by M. Rdjoux. 

 Formerly, when porcelain was decorated with gilding 

 alone, the ornamentation was limited to the production 

 of a pattern by the greater or less relief of the gold, and 

 by its being burnished or left dead. Even the thinnest 

 part of the gilding was opaque. No delicate effects 

 could be produced, rnd the style was suited rather for an 

 abundant display of birbaric wealth than for refinement 

 of expression. 



The new process enables the gilding to be put on so 

 thinly and transparently that the most delicate effects of 

 light and shade can be produced. It is, however, 

 applicable only to vases of gros bleu colour, that is, 

 to vases coloured with oxide of cobalt. Upon this ground 

 the pattern is drawn with a pigment composed of oxide of 

 aluminium. This is then subjected to a firing which fuses 

 the oxides together, and a brown surface results. This 

 surface is found to be more suitable than any other known 

 for the reception of the gold paste, which can be laid on 

 in a thin film, and then, further, by subsequent removal, 

 can be made to give great transparency. This property 

 of the brown surface is not destroyed by being tinted 

 before the gilding, so that it is possible to tint it with 

 different colours which shall show through. A further 

 variation is very frequently obtained by changing the 

 tone of the gold by mixing it with alloys. This admirable 

 effect of transparency has not been produced by any 

 other means, and the first piece made (with many subse- 

 quent) is exhibited. 



Another of the processes invented at Sevres is that of 

 enamelling on pdte-teiidre body. In this the colours are 

 applied in powder in the same way as in enamelling on 

 metal, and are fused at a very low temperature. They 

 have more body and are more decided than are those 

 produced by the older enamelling process. On some of 

 the vases shown at the Exhibition the white ground seen 

 is not that of the creamy pdte-tendre body, but the pearl 

 white of the stanniferous enamel. 



Other recent improvements which should find a place 

 in a more technical and exhaustive notice have been 

 illustrated at the Exhibition. It may be mentioned that 

 other nations are striving to adapt some of the traditionally 

 recognised styles and their method of manufacture. 



We may, in conclusion, refer to a small but important 

 exhibition of porcelain, allant-att-feu, useful for laboratory 

 as well as for domestic use. It is a very good white, thin 

 and hard, and will bear high temperatures if the changes 

 are not too sudden. 



SUN-SPOTS, ATMOSPHERIC PRESSURE, AND\ 

 THE SUN'S HEAT 



THE question whether the atmospheric pressure varies 

 with the spotted surface of the sun was noticed by 

 me in a paper on the Isobars within the British Isles. I 

 could not, however, find any appearance of a decennial 

 law in the yearly mean pressures : such a relation pre- 

 sented itself however in the varying directions of the 

 isobars \Proc. Roy. Soc, 1877, p. 599). The yearly mean 

 pressures in our latitudes are subject to large irregular 

 variations, and several decennial periods would be re- 

 quisite before these could be neutralised in the decennial 

 means. As the irregularities are much smaller within 

 the tropics, I did not fail to examine the yearly means for 

 India which were in my possession at the time ; and I 

 found their variations very small and apparently without 

 any relation to the decennial period. Mr. F. Chambers's 

 interesting letter to Nature (vol. xviii. p. 567) has 



