Fabrication of Crayons, 409 



caufe tlie leaft alteration occafions a confiderable difference in the quality of the pafle. 

 It is particularly neceffary to guai-d againft thofe errors which may happen from ine- 

 vitable diminution, during the time of the manipulation. The beft way to prevent this, 

 will be to afcertain by experiments, the quantity of water and grinded ochre which the 

 folutions may contain before mixing them. 



By means of the quantities ftated in the following table for each of thofe kinds of 

 crayons, it will be eafy to know the proportional quantities of gum, glue, or foap, 

 which may be employed for a determinate weight of ochre or red oxide of' iron. 



Subjlances to be employed, with their quantities and refults. 



No. 1. 



f Thefe crayons are very friable, but 



_ , , . , . . 1 they may be ufed for large drawings. 



Dry ochre, or red oxide of iron 10. gram. ,' r^^^^^ ^^^^^;^^ ^,^^ ,^.^jj |j,j^ , ^ 



l.Qtigram. } „, tfi.,/„ u„..r„j .i5„ :ii „1. u...i 



Dry gum arabic 



No. 2. 

 Ochre, &c. 

 Gum 



No. 3. 

 Ochre 

 Gum 

 Or Hill better with 



No. 4. 



Ochre 



Gum 



° ■ [ of gum. If lefs be ufed they will not have 

 V^fufficicnt confiftence to be of any ufe. 



10. gram, f Soft crayons, rather friable, and ex- 

 0.363 gram. \ cellent for large drawings. 



10. gram 

 0.415 gram 

 0.441 gram 



;} 



Smooth and folid crayons, fit for com- 

 mon ufe. 



10. gram, / 

 0^67 gram. \ 



Soft firm crayons, for drawings which 

 require delicacy and precifion. 



No. 5. 

 Ochre 

 Gum 



10. gram. 

 0.519 gram. 



/ Very firm crayons, fit for fmall draw- 

 ls ings, which require to be highly finiflied. 



No. 6. 



Ochre 

 Gum 



10. gram. 

 0.571 gram. 



{ 



1. \j& 



Crayons almofl; too hard to be ufed. 

 This is the maximum of gum that can 

 be employed in their compofitiou. 



No. 7. 

 Ochre . . 10. gram. C Thefe crayons are of a darker colour 



Qunj . . . 0.380 gram. < than the others mentioned ; they are of 



White dryed Soap . . 0.519 gram, (.a very hard confiftence, and foft to the 

 touch ; but all crayons into whofe compofition any foap enters, have the defeft of 

 making ftrokes which fliine too much when retouched. None of my experiments with 

 foap fucceeded. Thefe crayons very much referable thofe of the compofition of Cj 



Defmantt. 



Chemical 



