How to bleach hair platinum blonde

Mix equal parts powdered bleach (such as Wella Blondor or Clairol Basic White) and developer until it reaches a creamy consistency.  Those with light-colored hair should use 20-volume developer.  For darker hair use 30-volume developer.  40-volume developer should only be used by professionals, since it increases the risk of hair damage.

Beginning in the nape area, apply bleach mixture with a brush from the ends to the mid-shaft.  Continue working from the back of the head to the front.  Now go back and apply the bleach mixture to the root area until all of the hair is coated with the bleach.  Bleach processes faster near the scalp due to body heat.

Cover the hair with a plastic cap in order to prevent the bleach from drying out.  Check the hair every ten minutes by wiping the bleach from a small section of the hair and observing the color.  Once the hair has been lightened to very pale shade of yellow blonde, processing is complete.  For most people, this should take 10-20 minutes. 

Shampoo the hair until all traces of the bleach are removed.  This may take 2-3 shampoos.  Do not condition the hair at this point.  If the hair is still "brassy" (orange-yellow), dry the hair and re-apply the bleach until the pale yellow blonde color is achieved.

While the hair is wet, apply a violet-based toner.  A toner is a semi-permanent pastel dye which will neutralize any remaining yellow tones in the hair.  Most toners are mixed one part dye to two parts activator liquid.  Check for specific manufacturer's directions prior to mixing.  Leave the toner on the hair for no more than 15 minutes.  Once the hair no longer appears to contain any yellow tones, rinse the toner out (do not shampoo) and apply conditioner.