The cup I used for Complan turned brown – is this something I should be concerned about?
If left unwashed, a cup that contained Complan may form some brown residue. Complan contains iron and in certain circumstances this can react with organic compounds, which are then absorbed into ceramic materials. These stains can be removed using a proprietary cleaner (such as a Stain Devil), which contains EDTA. This forms a chelate with the iron making it soluble.