The table wants you to work out the proportion of distilled water to the proportion of peroxide to get the reduced strength of peroxide.
1. Convert 40vol to 30vol with distilled water.
40v minus 30v = 10 so
30 - 10 take off the 0’s and you’ve got 3 - 1
so the answer is 3 parts 40vol to 1 part water. (In the table it’s 1 part water to 3 parts H2O2)
In practical terms, if you need to make 60ml of developer then you need 45ml 40v and 15ml water.
You divide the total amount of ml required (60ml) by the total number of 4 parts, so each part is 15ml.
2. Convert 30vol to 20 vol following the above formula
30 - 20 = 10
20 - 10
2 - 1 or 2 parts 30vol peroxide to 1 part water
Again, for 60ml developer, you mix 40ml 30v with 20ml water.
or 60ml divide by 3 parts so each part is 20ml.
Additional info:
The problem with using distilled water is that it works mathematically, but in practice it makes the mixture too runny and so you're more likely to get bleeding within a foil. You can also use tap water but Tap water in some hard water areas can contain a high concentration of metals and if you remember your Incompatibility Test, you’ll remember what happens to hair that contains metals or metallic salts when applying bleach or tint...
You can also mix your developer with a basic conditioner in place of water as that will be 0% peroxide, the same as water, but won't make the mixture as runny.
I used to add info. like this to my Notes app on my phone that I could refer to it when needed. You’ll find that in a salon there’s sometimes an occasion when you want to dilute your developer and it’s handy to have a quick reference guide to assist you.
Also, be aware that you cannot increase the strength of peroxide by mixing different strengths, only dilute it.
So, 3 parts 10vol will only ever be 10vol strength. It will never be 30vol!
18% or 60vol is only sold in a few places these days but it used to be widely used back in the eighties...! Modern tints and bleach formulas don't require the use of high vol peroxides but you might hear about these high strength formulas from more experienced older hairdressers.
Finally, some tints are oil based so their developers are also oil based. If you diluted their developer with water, you'd get a strange emulsion that won't mix properly and compromise the service.
Hope this has helped?
@HairByMaisyVoice
