Going blonde - Majirel

Definitely use the color remover before considering any bleach. They can be used up to three times but they can dry the hair so remember to deep condition it after. Once you know what your base is, you can move on to bleaching or using the majirel you want.
Before using anything with peroxide , you will need to assess the condition of your hair. Having previously used 40vol, you need to be very careful with what you put on your hair as 40vol is way too strong peroxide and really shouldn't be used at all. Personally I think it shouldn't be sold at all as it is completely unnecessary and way too damaging.
The instructions for Majirel recommend using either 20 or 30 vol but since you have previously processed hair, I recommend you stick to the 20 vol or even 10 vol if you can.

I know 40vol is waaaaay harsh.

I'm decidedly lucky in that the majicontrast seems to counteracted the damage and the hair, apart from a few split ends, is in pretty good shape. However, going blonde, I will definitely, be using the 20vol or, like you say, 10vol otherwise I'll look like a fizzed out haystack!

So am I right in saying it's just a case of picking which shade of Majirel I want and mixing it with (100ml) peroxide?

Thanks for your help with this!  🙂

If you used majicontrast with 40 vol, your hair will be pretty light once you take the red out. So start with colour removers and see what they leave you with.
Hi lift blondes are not the best choice for lightening very dark hair, you will get more lift and less damage with a really good bleach that you can use with lower vol peroxide