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What do the Developer Numbers really mean?

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Category: Hair Talk
Forum Name: Hair Color
Forum Description: The tricks and tribulations of changing your hair color
Printed Date: April 19 2018 at 10:45am

Topic: What do the Developer Numbers really mean?
Posted By: bnbivi00
Subject: What do the Developer Numbers really mean?
Date Posted: January 05 2007 at 7:49am
I went to school and was always told that the developer volumes (10, 20, 30, 40) mean intensity.  10 is the lowest intensity and 40 (well, now 50) is the highest intesity.  Well, a friend of mine went to cosmo school in Cali and she was taught that 10 Volume means that it is active for 10 minutes and 20 Volume means it is active for 20 minutes and so on.  SO, you could use 10 Volume on someones head using foils and the solution is only good for 10 minutes.  In my experience, that isn't true.  That is why I foil on top first because the longer the solution stays on the head, the lighter it gets.  Also, she said that if I used bleach with on someones head with half using 10V and the other half using 40V but only left it in for 10 minutes, I would reach the same change.  Again, I haven't seen that.
Can someone with lots of knowledge on why the numbers 10, 20, 30, and 40 are used please help me out here?

Posted By: chinastop
Date Posted: January 05 2007 at 3:58pm
Mixes are good for one hour and a half.

IT depends on what result you want.  Since the time limit is the same, you choose it based on the number of levels you want to lift.  10 lifts 1 level, 20 lifts 2, etc.  30 vol for example will lift 3 volumes quickly and then plateau out to lift at the same speed of 10 vol (more slowly). So I think she's right about the 10v and 40v thing.

10 developer is 3%, 20 is 6%, 30 is 9%, 40 is 12% HP.

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