Ammonia free hair dye and grey coverage

[jolo2007]

Can any one help me with this.
I've been told that to cover grey hair when using ammonia free hair dye, it's good to use 30vol as it will open the cuticle more and is is ok to use as the rules are slightly different to traditional hair dye because of the no ammonia content.

 

[kevinm]

Unfortunately it depends on the range, I believe that some companies have started using alkaline agents in their developers as well as the tint to aid with coverage but it would vary on a company by company basis.

Also increasing the strength of the developer wouldnt aid in coverage (in most cases). The best advice would be to cointact the manufacturer or give some more details about brands and previous experiences here and I'm sure that someone will be able to help out.