It's all about the Dominant present - see one of my posts above.

Oh, i'll have to research that. Thanks!:)

Actually the alchemy works like this:

You need to find a fire and meditate to access the panel.
In the panel you can select what you want to create.
YOu need a "base" vial to create any potions, cheaper vials can be base only for some potions, not all.
You can create a better "base" vial with a cheap vial and some ingredients if you have the formula (and you have it sure), sadly i play the italian version i duno what can be the name in english, in english can be something like "white jaeger".
When you create a potion, the pc offers a "random" pickup of elements for you, it works but its better if you pick up all the ingredients by hand, as someone wrote before, there are 3 different dominant you can create, the black one, the red one and the white one.
To have a potion with "white" dominant, called albedo, you need to use all the elements with the white dominant, quite simple even if boring if you want to create many.

The pc seem not good to pick up elements to create potions with any dominant, so you will need to select manually always all the elements to create the potion you want.
Tbh the game offers a large number of potions but you will need no more then 3-4 to perform good.
The one with healing effect over time
The one with healing effect immediate
The one with increased max resistance effect
The one to see in the dark

All the rest is just more then optional or needed for specific quests.
Also for my personal experience its better to create all healing pots albedo (white dominant) as you can use more if needed without being too intoxicated, and the "see in dark and resitance pots with red dominant.
I never crafted black dominant pots.
Last thing ofc to prevent to have an inventory full of different pots, create and stack up always the same dominant.

Edit : About the fact to create wrong ptions, it can happen if you select one or more wrong elements manually, it never happens to have any wrong elements selection by the pc auto choice, but as wrote before the pc will not check any dominant or the rariry of an element to decide what to use.
It never happened to me anyway to create any alcholic beverage by mistake, it just tells "unknown potion" to me, so check about it prolly the beverage was in the inventory also before.

Second edit:
There is a minor issue that may be misleading, when you create the "better base potion", assuming its called "white jeager", starting with a low cost vial combined with some herbs, if you select again the same pattern, the pc dont do any distinction between crap vials and the "better vial" you just created as base.
So it can be a little issue, as if you create many "better base vial" using the pc auto choice, can happen that the pc continue to auto select the better vial you just created as base, as result you are wasting elements cause you only have in bag the same "base vial" at the end.
To prevent this, you need to check and in case manually select the base vial using one of the cheap bought or found, preventing the pc to use the vial you just created.

Usually what I do is I select the potion from the list, click once, and the game automatically chooses a base and ingredients for me, but it hasn't actually mixed the potion yet. Then, if I want a specific dominant substance, I substitute out the ingredients the game picked for the ones I want to use. This way I don't have to check the formula.

To the OP: Mixing Swallow requires four ingredients, so not all alcoholic bases are good enough. Make sure you either have one that can support four ingredients ("high quality potion base") or you mix a White Gull first, and then use the White Gull as the base for the Swallow.

Also, after you've selected which potions you want to mix, you will have to actually initiate meditation for an hour to mix them.

Oh, and make sure you have a spare inventory spot for the potion, otherwise Geralt will drop it on the ground.

Correct me if I'm wrong, but I think "Albedo" affects the toxicity of subsequent potions you ingest -- for the next hour of game time. This means you can use the lasting Albedo to take further potions, so taking Albedo early pays off.

My tactic is to use a potion with Albedo first, then other potions; for example, Tawny Owl with Albedo, then Swallow with Nigredo, and if I need it in a tough battle, White Raffard's with Rubedo. These are all potions you can make in quantity, by early in Act II.

You can. That's why I've made and printed a nice spreadsheet for all subsequent playthroughs ;)

Hello again
Sorry for late reply, I havent been home the last days

Here is a screenshot of what I get if I mix Swallow

Yeah, the plum cordial that you're seeing is what you're going to use as the base for the potion. Basically the game is saying "it's it OK if I use this plum cordial and these four ingredients to make the potion?" and then you have to click the "mix" button to confirm that that's OK. if you wanted to use different ingredients to make the potion (for example if you wanted to have a dominant substance like nigredo, rubedo or albedo) then you can swap out the ingredients that showed up automatically for some different ones that have those substances in them.

Once you've confirmed by hitting the "mix" button, you will see that your "meditation time" has increased to one hour. If you click the hourglass in the bottom left, Geralt will meditate for an hour and make the potion. But, before you do that, if you want to mix more potions, you can.... Geralt can mix as many as he wants in that hour. So you can mix a whole bunch before you hit the hourglass button.