Random mixes very very rarely produce anything useful. There are a limited number of useful potions compared to the total possible with one "secret" recipe available on the wiki and walkthroughs out there. The ingredients will generally be wasted unless you use the correct combinations. If the recipe is followed incorrectly you will end up with a "unknown potion" and when drunk a "failed potion".The recipes are static in the game, so if you already know the combinations from a previous play-through, you will re-discover them by experimentation later in a later play-through. For example, White Gull is ALWAYS Vitriol + Vitriol + Rebis.However, something I found out about mass-producing potions without the recipe learned (or "blind") is that if you save the game and reload with an inventory of unknown potions, any secondary element effects will be lost when the potion is finally drunk and "learned". Be warned.