This is a two-part issue. Sometimes the hair is not yellow, but in fact, has been bleached to orange. Iced Platinum would have trouble neutralising orange – it would knock some of the edge off the overall tone, but it just could not fully neutralise orange from the hair. Remember, Iced Platinum is an anti-yellow. So, the first question you need to ask is: how bright is the yellow? Is it a yellow-brassy colour? Or is it more of an orange or a copper? If it’s more of an orange or a copper, this means the hair has too much depth to go blonde and no pale-yellow base to enable a neutralisation to platinum. Therefore, you need to re-lighten the hair (further) to obtain a yellow base that would tone to blonde.
By contrast, your hair may be sufficiently lightened and displaying a pale yellow that could tone, however Iced Platinum has been unable to enter the hair. This issue occurs due to barriers on the hair’s surface, such as conditioning polymers, styling residue and silicones. You will find this problem is most prominent when a box lightening product (not a bleach) has been used. Such colourant-based lighteners use silicones that block out the hair and prevent it from toning. Likewise, many home bleach kits contain rich silicone-based finishing conditioners that cause a block on the hair and prevent toning from happening. In these instances, treat the hair several times in Precolour Clarifier and then attempt to use Iced Platinum again. After clarifying, the hair should have opened, and the neutralising pigments will be able to enter and evoke change.