Bu dhe M r, or Great Yellow. With this they dye their linen and fine woolen stuffs with different degrees of colour and fix the colour with urine. The yellow thus obtained is bright and lasting. In a recent workshop on natural dyes, we got a yellow very similar to that yielded by weld using the leaves of the sweetgum tree, using alum as a mordant. The type of mordant used will usually affect the end color of the fabric.
Stale urine is called fual , or graith in Scotland.
Probably used from the earliest times. Iron could be obtained from certain bogs or iron ore. Oak-galls were sometimes used to dull the colour. They were usually gathered in July and August, dried in the sun, and used without mordants to dye wool in an iron dyepot. Ammonia can be used for modern dyeing instead.