What can I use instead of alum?

“Instead of aluminum salts, you can use plants as mordants: symplocos (plant alumina), tannin-rich plants (gallnut, sumac, birch bark…), and oxalic-rich leaves (rhubarb, sorrel, beetroot leaves…). At Teinture Sauvage this is how I mordant wool, silk, linen, and cotton. The comparison table summarizes the three types.”