* The specific hair dye you're using: Follow the instructions on the dye packaging exactly. Different brands and formulas require different ratios of developer to dye.
* Your hair's length and thickness: More hair will need more product to ensure complete coverage.
* Desired lift: 20 volume developer provides a moderate lift (1-2 levels). If you're just depositing color or going only slightly lighter, it's a good choice.
General Guidelines (but always refer to your dye instructions first):
* Most permanent hair dyes: Typically use a 1:1 ratio of dye to developer. For example, if the dye instructions say to mix equal parts of dye and developer, and you're using 2 ounces of dye, you would use 2 ounces of 20 volume developer.
* For a thick consistency (which is good for even application): Stick to a 1:1 ratio.
Important Considerations:
* Developer Strength: 20 volume developer lifts the hair slightly while depositing color. It's generally a safe choice for achieving vibrant red shades without causing excessive damage.
* Always do a strand test: Before applying the dye to your entire head, test it on a small, hidden section of your hair. This will show you how the color will look and ensure you don't have any adverse reactions.
* Wear gloves: Protect your hands from staining.
* Protect your clothes and work surface: Hair dye can stain easily.
In Summary:
The best advice is to meticulously read and follow the instructions that come with your specific red hair dye. That will tell you the exact amount of developer to use. If you're still unsure, consult a professional hairstylist. They can assess your hair and recommend the appropriate products and techniques.