It will only fail, if you try an invalid combination, what exactly do you combine? If two small poison bottles, it should give you one medium, if you combine two medium, it should give you one large, if you then combine two large, you should get one Giant Poison bottle (same with healing potions). Once you craft any of this, it should get into the recipe list, then you should be able to craft from there directly. Recipes never fail, unless you don't have the numbers of ingredients needed, then it should be greyed out. I don't really know, where's the issue.
