Progressive dyes often known by the brand name 'grecian formula' are a method of hair colouring to disguise or eliminate gray hair using a clear solution of metallic salts.
This solution of metallic salts is applied daily, gradually allowing the salts to absorb oxygen from the air causing chemical changes that will result in darker hair due to staining.
Lead, bismuth, antimony, iron and silver were all among the metallic salts originally used in progressive dye formulas. However many proved to be toxic and iron and silver salts (still occasionally used) can react violently with perming and tinting chemicals causing the hair to change colour or fizz and burn.
The use of progressive type dyes is generally not recommended for women that tend to do a lot more to their hair than their male counter parts and you definitely won't find them on offer at your local salon.
Visitors to this page also went to allergies to hair dyes and henna.