You must have a small corresponding pattern that you intend for purple, which at times you must put into the blue vat to regulate the depth of the archil ground, as the purple is a compound colour, arising from the blue of the indigo and the red of the archil. When the red of the archil is deep enough, you must wash it off and put it into the blue vat with proper precaution. The fulness of the archil ground and the depth of the blue, must be regulated according to the patterns which are to be matched.
To dye silk LILAC.
Lilac is and should be a bright light shade of violet or purple; to give it the blue requires great management. The vats being generally too strong, it is best to mix a little of the new rich vat with some pearl-ash in clean cold water, and so prepare a liquor on purpose, by which the lilacs may be blued or reddened at pleasure. When this liquor is first mixed it becomes of a green colour; the silks therefore should not be dipped till the liquor begins to lose its green colour and inclines to blue. Pearl-ash added to this liquor helps to blue the archil, because the effect of the alkali upon red is to render it violet.
Another process for LILAC.
Consists in simply using the chemical blue with archil according to the shade required.
Another process for dyeing muslin, &c. LILAC.
This is accomplished by mixing the neutralized chemic blue for cotton with the pink dye of safflower, according to the shade required.
To dye silk a VIOLET or PURPLE with Logwood.
The silk should be alumed and washed. The logwood should be boiled in large quantities like fustic, as as directed for green; but it should not be kept longer than two or three weeks; it is far better used cold than hot.