Tea or clay will "dye" the cloth and make it look aged but you do not want your tea too strong or you will end up with a tan to brown piece of cloth that has obviously been dyed. Try starting with tea that is drinkable and vary the dye time. You can always make stronger tea or soak it longer if the first pot does not give you the aged look that you want. Plain old gummy mud will stain your fabric, too. It, too, will require a bit of experimentation to get the aged look that you want and you will want to rinse the fabric thoroughly to remove all traces of the grit. Walnut hulls make an excellent dye but will require care not to get the color too dark. Once you get the aged look that you want, use an iron to set the color in your fabric. Just iron it as though you were simply removing the wrinkles and the heat will set the color.