* Demi-Permanent Color and Developer Strength: Demi-permanent colors are designed to deposit color only. They typically use low-volume developers (6-10 volume) that open the hair cuticle just enough for the color molecules to enter. A 15 volume developer is more appropriate for permanent colors where the goal is to lift the natural color and deposit new color.
* Grey Coverage: Demi-permanent colors can *blend* greys, making them less noticeable, but they don't typically provide 100% opaque coverage, especially on resistant greys. They rely on staining the hair rather than fully replacing the pigment. Permanent colors are better for full grey coverage because they can lift the cuticle and deposit pigment within the hair shaft. The higher volume developers needed for permanent hair color help with grey coverage.
* Lifting Base Color: Demi-permanent color, even with a slightly higher volume developer than recommended (15 vol in this case), will *not* provide significant lift to your base color. A 15 volume developer is designed for *slight* lift when paired with permanent hair color. Demi-permanent formulations are just not designed to lighten the natural pigment of the hair.
* Ammonia-Free vs. Lifting: Ammonia is an alkalizing agent that helps to open the hair cuticle and allow color and lifting agents (like peroxide) to penetrate. While ammonia-free products are gentler, they often lack the power needed for significant lifting. They typically rely on other alkalizing agents, which may not be as effective at lifting in conjunction with demi-permanent hair color.
In Summary:
* Demi-permanent color + low volume developer (6-10 vol): Best for blending greys, adding tone, and enhancing existing color without significant lift.
* Permanent color + higher volume developer (20 vol+): Best for full grey coverage and lifting the base color.
What to do for your desired results:
If you want to cover and blend greys, while also slightly lifting the base, I would recommend using a low volume permanent hair color and a 20 volume developer. This will ensure adequate grey coverage and a subtle lift. If the greys are very resistant, you may want to consider a permanent hair color that is specifically formulated for grey coverage.
Always follow the manufacturer's instructions for the specific hair color product you are using. Do a strand test before applying the color to your entire head to ensure you achieve the desired result.
Disclaimer: This information is for general guidance only. I am not a hair stylist, and professional advice should be sought for specific hair coloring needs.