Direct dye covers an extremely wide variety of molecules that are already intensely colored. They have a wide range of usage in textiles, plastics, cosmetics and in hair dyes.
Direct dyes don’t penetrate very deeply into hair. Because there is little penetration, it is easily shampooed out. This is why we often refer to products that contain mainly direct dyes as temporary. Because of their special vibrancy they are used to provide additional color intensity and staining.
The Kao Research Laboratories in Japan and Germany have developed different direct dye technologies with one purpose: to make hair color brighter, more colourful. They have solved many of the different problems colorists all over the world face so that we’re now in the position to distinguish between different direct dyes technologies.
Direct dyes have several things in common:
They are completely developed molecules and ready for immediate use.
They don’t require activation by mixing with a developer.
They grab onto hair because of different forces such as electromagnetic charges.
They tend to attach mainly at the outer layers, or cuticle, of hair.
They are very color intense and vibrant.
Mixing is very easy as only the rules of subtractive color mix apply.
Conventional, common direct dyes are positively (+) charged molecules that are attracted to negatively (-) charged areas of hair. These direct dyes are bigger than couplers and precursors and therefore are not able to penetrate that deep into the hair. They tend to cluster and, by doing so, get even bigger.
Mostly used in acidic or neutral products, conventional direct dyes don’t swell the hair in the way oxidative/alkaline products do. The acidic or neutral environment is another barrier for the conventional direct dye technology to penetrate deep inside the hair. This makes conventional direct dyes not as durable as oxidative dyes or the Special Kao developed direct dye technologies.
To increase intensity, theses dyes need a more porous hair structure, allowing for deeper penetration.
Other factors for durability and intensity are a longer processing time and the amount of dyes. The more dye and the longer the processing time, the more dyes are attracted to the hair.
One of the biggest inventions in hair color is Elumen.
As opposed to direct color dyes using conventional technology, Elumen works with acidic, negatively charged direct dyes and a pH value of 3.0. The natural lactic acid in the color mixture is responsible for this acidic environment.
The special technology transforms the charge of the hair. An excess cationic (+) charge is created and because the Elumen dyes are anionic (-) charged and a type of “pulling effect” is exerted, literally drawing the negative charged Elumen dyes,into the hair. A simulated magnetic, electrostatic attraction occurs, attaching the negatively charged color dyes firmly and permanently to the already positively charged hair.
Learn more about Color Theory here.