Any ideas on how to remove red clay from a cotton uniform?
Clay should be dissolved in a strong solution of detergent and water, clothing or any type of pre-treater like Shout. If you leave a red stain, does not wash in hot water, you can set most stains. As the matter is a uniform, it is likely it very difficult to wash clothes without losing its color. You can try a little diluted in an inconspicuous place, like a hem of his shirt and see if the material is colorfast. If color runs, you can try a bleach (peroxide) and Snowy.
Freddie Hubbard “Red Clay” (1970)