Mr. Rawlinsotfs Colour Mill. 
Reference to the Engraving ( Plate 18) of an improved 
Mill for grinding Indigo , or other dry Colours. 
Fig. 4. L represents a mortar made of marble or bard 
stone ; one made in the common way will answer. M, a 
muller or grinder, nearly in the form of a pear, in the upper 
part of which an iron axis is firmly fixed, which axis, at 
the parts NN, turns in grooves or slits, cut in two pieces 
of oak projecting horizontally from a wall, and when the 
axis is at work, are secured in the grooves by iron pins, 
00. P, the handle, which forms a part of the axis, 
and by which the grinder is worked. Q, the wall in 
which the oak pieces NN are fixed. P, a weight 
which may occasionally be added, if more power is 
wanted. 
Fig. 5, shows the muller or grinder, with its axis 
separate from the other machinery ; its bottom should 
be made to fit the mortar. S is a groove cut through the 
stone. 
On grinding indigo, or such substance, in a dry state, 
in this mill, the muller being placed in the mortar, and 
secured in the oak pieces by the pins, the indigo to be 
ground is thrown above the muller into tbe mortar; on 
turning the handle of the axis, the indigo in lumps falls 
into the groove cut through the muller, and is from 
thence drawn under the action of the muller, and pro- 
pelled to its outer edge within the mortar, from whence 
the coarser particles again fall into the groove of the 
muller, and are again ground under it ; which operation 
is continued, till the whole of it is ground to an impalpa- 
ble powder; the muller is then easily removed, and the 
colour taken out. 
A wood cover, in two halves, with a hole for the axis, 
is usually placed upon the mortar, during the operation^ 
