1817.) On the Ancient Purpurissum. 135 
and on a probable means of procuring a substitute for purpurissum 
in the present day, appear worthy of a place in your Annals, they 
are much at your service, and I remain, 
Sir, your most obedient humble servant, 
Glasgow, Nov. 22, 1816. A Consrant READER. 
eo 
I believe that a good and egonomical pigment of a carmine red 
colour has remained a desideratum amongst artists since the time 
when the knowledge of the method of preparing the purpurissum 
of the ancients became lost to the world. Our highest class of 
artists, the painters in oil colours, are precluded in a great degree 
from the use of carmine by the enormous expense of procuring it 
in quantity, and by its difficulty in mixing with oil. For these 
reasons, I believe, they are compelled to substitute for the use of 
carmine the yellower reds, such as vermilion, and ochre, and to 
reduce them to a tinge fit for the representation of the various lines 
of the human skin by a mixture of blue. It is evident, however, 
that this must prove but a dusky imitation of nature; and as de-. 
tailing an experiment to procure a substitute for carmine, perhaps 
you may deem this letter worthy of a place in your Annals, although 
many of your readers may consider its contents of a trifling descrip- 
tion. Chaptal supposes that the ancient purpurissum was obtained 
by dyeing the creta argentaria with a decoction of madder. This, 
however, I should conceive to be a difficult process; and one by 
which a pigment of a vivid red could not be obtained. Could such 
a colour, however, as what we now impart to cotton by the Turkey 
red process be given to a pigment, an object of value and import- 
ance would certainly be gained, by procuring a colour fit for the 
use of painters, indelible, and brilliant. A probable means of 
effecting this was suggested to me in reading Messrs. Kirby and 
Spence’s work upon Entomology. The account given in that work 
of the nature and habits of the tinea tapetzella, or clothe’s moth, 
impressed me with an opinion that the larvee of this insect might be 
made an essential accessary in the preparing of purpurissum. 
Messrs. Kirby and Spence say that pigments of a brilliant hue are 
obtained from the excrements of the larv@ of the clothe’s moth by 
feeding them on woollen cloth of the colour of the paint wanted. 
Now it struck me that, could these insects be nourished on cotton 
dyed Turkey red, their excrements might serve for preparing a 
colour superior to carmine. I accordingly procured some of the 
larvee, and shut them up in a large jar, which I filled with cotton 
dyed ‘Turkey red. At the end of a fortnight I opened the jar, and 
found the larva alive, though apparently more languid than when 
first shut up. They had, however, fed on the cotton, and their 
excrements were of a vivid red. 1 allowed the jar afterwards to 
remain shut for the space of four months, being too much busied 
by other avocations to think of attending to it. When 1 did open 
