1818.] On the various Uses of the Septaria. 39 



On various Uses of the Septaria. 



The septaria, Indus Helmontii, or loam-stone, is usually found 

 accompanying the London clay, in nodules of different foj*ms 

 and sizes, and is of a pale yellow colour. It is procured on the 

 banks of the Thames at low water, in the island of Shepey, and 

 in various other places ; but the best, I believe, is found on the 

 estate of Lord Mulgrave, near Whitby, and at a distance from 

 the sea shore, where it has not been impregnated with the salt 

 water. This is employed for Roman cement, after being calcined 

 to an olive-brown colour, and ground to powder : it does not 

 effloresce, as is too commonly the case with such as has been 

 obtained from the sea shore ; and if it be mixed up for use with 

 water containing a dilute solution of sulphate of iron, it will be- 

 come very considerably harder, and more durable. This, I be- 

 lieve, is nearly the only use it has hitherto been put to in this 

 country ; but it is capable of being employed in a variety of other 

 ways, with very considerable advantage ; and, particularly in fine 

 casting, of gold, silver, or molu, &c. where it forms a most excel- 

 lent facing, after being slightly calcined till it is of a red colour 

 and then finely powdered ; in this state it lines the moulds when 

 it is sifted over them, and the impression of the patterns or models 

 is again taken upon it with an exceedingly smooth coating : it 

 never burns through by the heat of the melted metal, and gives 

 an extraordinary degree of sharpness to the casts. Indeed, I 

 have no doubt that by the use of it minute casts in iron may be 

 made from cameos, &c. equally perfect with those lately brought 

 into this country from Germany, and which are so deservedly 

 admired. It will also be found useful in taking impressions of 

 gems in glass, in the manner of Tassie, when used instead of 

 Tripoli ; which earth it also very much resembles in its property 

 of polishing gold, silver, ivory, varnished wares, &c. ; after being 

 calcined to an olive-brown colour and levigated, and then either 

 finely sifted, or, which is better, washed over, letting it remain 

 suspended in the water for half a minute ; when it will be found 

 to give a beautiful black lustre to articles of gold or silver, by 

 rubbing them with a little of it, applied upon the palm of the 

 hand, or the smooth side of leather; and indeed it forms an 

 excellent plate powder for domestic use. 



These are only a few of the many uses the septaria has been 

 put to ; but enough, I should presume, are pointed out, to call 

 the attention of your readers to this valuable production, and to 

 ib> more extensive employment in the arts of this countiy. 



