diff --git a/docs/files/recipes/mordants_tannins.md b/docs/files/recipes/mordants_tannins.md
index 168edb167954c199dd1c918378779000c14af4ed..74d3cb80645adb29626a6c512ca0eff5bd9d8fc9 100644
--- a/docs/files/recipes/mordants_tannins.md
+++ b/docs/files/recipes/mordants_tannins.md
@@ -30,7 +30,7 @@ variable
 
 One of these or a combination (see below):
 
-* **Alum** (*aluminium sulphate*)
+* **Alum** (*potassium aluminium sulphate*)
 * **Cream of Tartar** *(tartaric acid)*
 * **Oak galls**, the whole nut, or powder (*galnut extract, gallotannic acid*)
 * **Soda ash** *(sodium carbonate)*