Manchester Memoirs, Vol. liii. (1909), No. 8. 19 



or away from the operator, in which case a series of small 

 flakes will be detached from the face opposite to the 

 direction of motion. This on a thin edge is tanta- 

 mount to re-sharpening, but it cannot be used on an edge 

 with a high cutting angle. 



(68) This effect can also be produced on a thin flint 

 edge by placing the flake flat on a smooth surface, and 

 drawing a knife blade, or a suitably shaped stone, along 

 the upper side of the edge under a moderate and even 

 downward pressure. 



(69) A fresh flint edge will serve for about 5 to 10 

 minutes when working on bone. This time will, of 

 course, var}' with the vigour with which the work is 

 carried out, and with the nature of the material operated 

 upon, but it is of the order named. 



(70) After being re-sharpened once, the edge will not 

 be found to serve for so long a time as in the first 

 instance, and the length of time of efficient service 

 diminishes with each subsequent re-sharpening. This is 

 due to the fact that the cutting edge is brought nearer 

 to the body of the tool with each operation of re-sharpen- 

 ing, and the angle of the cutting edge becomes corre- 

 spondingly less acute. {Fig. 6.) This factor limits the 

 number of times a tool may be re-sharpened to three or 

 four at the utmost, the cutting edge will then have been 

 worked back to a position where its angle will be a right 

 angle, and where the increased thickness of the tool 

 renders it impossible to detach small flakes, the blows 

 from the sharpener merely shattering the edge without 

 dislodging flakes. In this condition the tool must be 

 discarded, as it is useless for further work. 



(71) The effects of secondary flaking for re-sharpening 

 are cumulative, and the number of times the tool has 

 been re-sharpened before being rejected may consequently 



