Naturalis historia 35.46

35.46

Ab hoc maxima auctoritas Indico. ex India venit harundinum spumae adhaerescente limo. cum cernatur, nigrum, at in diluendo mixturam purpurae caeruleique mirabilem reddit. alterum genus eius est in purpurariis officinis innatans cortinis, et est purpurae spuma. qui adulterant, vero Indico tingunt stercora columbina aut cretam Selinusiam vel anulariam vitro inficiunt. probatur carbone; reddit enim quod sincerum est flammam excellentis purpurae et, dum fumat, odorem maris. ob id quidam e scopulis id colligi putant. pretium Indico $X$ XX in libras. in medicina Indicum rigores et impetus sedat siccatque ulcera.

CHAP. 27.—INDICUM. Next in esteem to this is indicum, a production of India, being a slime which adheres to the scum upon the reeds there. When powdered, it is black in appearance, but when diluted in water it yields a marvellous combination of purple and cæruleum. There is another kind, also, which floats upon the surface of the pans in the purple dye-houses, being the scum which rises upon the purple dye. Persons who adulterate it, stain pigeons' dung with genuine indicum, or else colour Selinusian earth, or anularian chalk with woad.
The proper way of testing indicum is by laying it on hot coals, that which is genuine producing a fine purple flame, and emitting a smell like that of sea-water while it smokes: hence it is that some are of opinion that it is gathered from the rocks on the sea-shore. The price of indicum is twenty denarii per pound. Used medicinally, it alleviates cold shiverings and defluxions, and acts as a desiccative upon sores.