Breaking the Base
Every colorist talks about “breaking the base” and few actually know what the term means. To clarify, it means to lift the natural haircolor one level or less; a slight and even barely perceptible amount. So, if the client has level 4 medium brown hair and you break the base, you are lightening her hair to a level 5 light brown or a shade in-between a 4 and a 5.
If your client is at all concerned about having red hair or looking brassy, do not break the base. 99.9% of the time you are going to pull warmth. For brunettes, it’s the dreaded red they don’t want to see, and for blondes it’s that hideous orange or gold undertone that will surface. It may not happen on the day the color is done, but weeks later that hair will be reddish or brassy.
Therefore, I ask, why would you want to do that? The answer of course, is that you want to produce warm haircolor as pictured on Holly Hunter. This is a perfect example of the results you can expect if you break the base. Very warm haircolor, which in some cases is appropriate. However, if your client is not happy with warmth, stay away from this technique.
If your client wants to be lighter than her natural haircolor then I recommend you foil in highlights. When done properly, you will not have to worry about unwanted natural remaining pigment rearing its ugly head and ruining your beautiful color creation. As always, it is your decision ultimately how you plan to lighten your client’s natural haircolor. Hopefully this bit of information will inform your decision.