Fabrication of Crayons, ' 40^. 



of thofe who have written on the compofition of thofe crayons, having mentioned the 

 quantity! of ingredients which ought to be employed, I have made a feries of experi- 

 ments on all the combinations poffible to be made with the fubftance%proper for that 

 fabrication. I have rejefted thofe produfls that have not anfwered the purpofe of my 

 enquiries, and I here offer thofe proceffes which have afforded fatisfaftory refults. 



Thefe crayons are compofed of foft ochre, which is an oxide or bog ore of iroH, 

 containing a mixture of earth, of the nature of the clays, which we called hematite. 

 They incorporate it with feme binding fubftance, fuch as lime, glue, or rofin, mixed 

 fometimes with foap, to take bff the hardnefs of the compofition. Inftead of the ochre, 

 called Sanguine in French ; the other ochres, fuch as thofe known by the name of brown- 

 red, or colcothar of vitriol may be ufed. In this cafe it is neceffary to chofe them 

 foft to the tovich, and of a lively colour ; thofe that are intended for fale being often 

 mixed with clay ; which gives the«n a yellowifh and dull colour, and ought confe. 

 quently to be avoided. 



I have made the experiment of incorporating thofe fubftances with the white of eggs 

 and the albumen of the blood ; but the crayons were not of a good quality. The 

 fofteft ochre fliould be taken and ground with pure water on a marble, as praftifed with 

 the colours ufed for painting, obferving to moiften it no more than may be abfolutely 

 neceffary, to facilitate the Aiding of the muller. 



When the operation of grinding in the large way becomes difficult and too cxpenfive, 

 another method may be praftlfed to divide the colouring matters. After pounding they 

 are fitted through a filk fieve, thendiluted with much v/ater in tubs, and after ftrong agi- 

 tation, left to fettle for a few minutes ; that is to fay, for the time fufficient to fuffer 

 the coarfeft parts to fall to the bottom. The %vater highly charged with the fined par- 

 ticles is then drawn off, and left to fettle for four and twenty hours, when the clear 

 water is alfo decanted off, A very fine powder is thus obtained. The coarfe remainder is 

 to be ground and treated in the fame manner till the whole mafs be reduced to a ftate of 

 extreme divifion. 



The gum, the glue, or the foap intended to give a fufficient degree of folidity to the 

 crayons, arc to be feparately diffolved, and the folutions worked up with the grinded 

 ochre. The mixture is then dried by expofing it to the fun, or before a fire by a very 

 moderate heat, taking care to ftir it often till the pafle ha? acquired the confiftence of 

 butter. 



The crayons are then to be fafliioned or moulded, which may be done in two ways. 

 The firft confifts in fpreading the pafte upon a board, in which a nmnber of channels 

 or half round groves are made, of an indeterminate length, but of a depth and width 

 proportioned to the fize of the crayons intended to be manufaftured. The fecond 

 method/'which is the beft, confifts in preffing the pafte through the pipe of a fyringe, 



3 G 2 whofe 



