15ml of dye should color approx. 20 kgs of wax to a medium shade. Suggested usage varies for each color & shade, and will also vary depending upon your wax formula and any additives you use.
Unfortunately the high percentage of dye required to produce black candles can result in problems with the wick. I am however introducing a black powder dye which produce black candles without wick issues.
Suggested usage Rates:
A medium shade is about 0.05% which equals approximately 8 drops of dye per 500g of wax.
For a dark shade, you should use 0.1% dye, which equals approximately 15 drops of dye per 500g of wax.
In order to produce black you will need to use 0.2% dye which is equivalent to 30 drops of dye per 500g of wax.
Please Note: These liquid dyes are very concentrated and have a strong odour. When used at normal usage rates this odour will not be noticeable once diluted with wax and fragrance oil in your candles.