some questions about dye and bleach

Ditch the 12%, its way too strong. You'll end up with chemical burns on your scalp. You'll want 6%/20vol.

What brand is the bleach powder? If it's something rubbish you'd be a lot better getting something good, we can advise there.

Is your hair currently dyed?

For the dye, just use a turquoise, maybe a bit of green, and add tiny bits of the dye until it looks like the colour you want. There's no set ratios, it's mostly done my eye. As you're going for a mint, you don't need to tone as the yellow will help you out.

12% peroxide is 40 volume, which is too strong to put on your scalp.
Swap it for 20 vol (6%)  it will be much safer.
The type of bleach powder you use is extremely important. Cheap generic drugstore bleaches give less lift and cause more damage than professional brands.
You will need to bleach it until it is a cream colour, like the inside of a banana peel. It will go red, then orange, then yellow before it reaches this shade.
Then you can put your blue dye on. How much you dilute it will depend on which brand/colour you choose. What dyes do you have access to, or are you ordering from here?

ETA Janine beat me to it

Well, it is bought at here: bleach!, the bleach powder.
It is a site for barbers, I think.

My mother does have 6 percent perioxide, so I can use that, if the 12 percent one is too dangerous. How long do I have to bleach it for, to have the desirable colour, or is this depending on the colour I have on my hair? The picture I just shown you in my first post is coloured hair.

And so I do not need a toner? And which brand would be the best?

I live in The Netherlands, so I have to be ordering online, I think.

if your hair is already dyed then you need to remove the old dye with a colour remover before attempting to bleach. You will not be able to achieve the lightest yellow you need for a pastel blue if you try to bleach out red dye.
The timing will be individual to your hair, do a strand test to find out how long you will need to leave the product on.
You don't need to tone separately if you bleach it light enough, the blue dye will be your toner.

Alright, thanks. 🙂 So I have to dillute the dye, if I want to have a lighter colour right? Just with a conditioner? If I want a babyblue colour, but really light, can I do that? I don't want it to be THAT exuberant, so.

What is a good website where I can both the dye and the colour remover?

Beeunique sells loads of different dyes, I am not sure what colour removers are available in the Netherlands.
You can dilute the dye until it is barely there, but it will only show up on a perfectly bleached base. Any remaining yellow tones in the hair will require a darker shade to cover them.

So if I want to have all of my hair the same colour, should I instead just tone it with a white toner?

Thanks.

Bleach your base to a lightest yellow colour, then put the blue dye on. the blue dye is the toner. White toners are just very dilute blue/purple dye

Alright, and you think the bleach powder is good?

I have no idea lol
If it were me i would buy a branded bleach.
You need to find a colour remover first though, otherwise your hair will go bright orange when bleached.

I have no idea lol
If it were me i would buy a branded bleach.
You need to find a colour remover first though, otherwise your hair will go bright orange when bleached.

Do you know any good color removers?

I don't know what is available in the Netherlands, but Colour B4, Decolour remover, JoBazz, Pro:Voke are all good brands available here in the UK.

And if you would pick one out of those, which one would you pick? Sorry to be nitpicking that much.

They are all good, it depends on what dye you have used and how much hair you have, I need 2 boxes so i would pick Pro:Voke because it is cheapest. They are all pretty much the same thing though. Colour B4 is probably the most widely available one.