Tin mordant gives the brightest colors with each of the natural dyes. The "Perfect Red" known as Scarlet is Cochineal on Tin. The bright oranges of Oriental carpets is Madder on Tin. The prettiest purple is Logwood on Tin.
Use at ½ ounce per pound of fabric (3%). Save the mordant bath and reuse by adding ¾ of the amount next time, (assume ¼ of what was added originally is still there). Some dyers like to add Cream of Tartar to the mordant bath (10 %) to buffer the Tin, which can be somewhat acid, and to soften wool fabric. (When re-using Tin mordant bath, do not keep adding Cream of Tartar, as it isn’t absorbed into the fabric.)
All mordants we supply and use are from naturally occurring minerals that come from the Earth. When the fabric biodegrades the minerals will return to the Earth from whence they came. There are no residuals left on the fabric as the minor amount of fixative is locked into the fibre.
For more information please see the article "The Myth of the Bad Mordant."