Dye
[2] The majority of natural dyes are derived from non-animal sources such as roots, berries, bark, leaves, wood, fungi and lichens.
[3] However, due to large-scale demand and technological improvements, most dyes used in the modern world are synthetically produced from substances such as petrochemicals.
The great majority of dyes are obtained in this way because of their superior cost, optical properties (color), and resilience (fastness, mordancy).
Scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes Tyrian purple and crimson kermes were highly prized luxury items in the ancient and medieval world.
Plant-based dyes such as woad, indigo, saffron, and madder were important trade goods in the economies of Asia and Europe.
Across Asia and Africa, patterned fabrics were produced using resist dyeing techniques to control the absorption of color in piece-dyed cloth.
[7] Dyed flax fibers have been found in the Republic of Georgia in a prehistoric cave dated to 36,000 BP.
By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, only few of which are used on a commercial scale.
He then reasoned that a sufficiently large dose could be injected to kill pathogenic microorganisms, if the dye did not affect other cells.
Ehrlich went on to use a compound to target syphilis, the first time a chemical was used in order to selectively kill bacteria in the body.
[17] The color of a dye is dependent upon the ability of the substance to absorb light within the visible region of the electromagnetic spectrum (380–750 nm).
It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.
Reactive dyes utilize a chromophore attached to a substituent that is capable of directly reacting with the fiber substrate.
The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fiber.
With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye.
This technique of dyeing is unique, in that the final color is controlled by the choice of the diazoic and coupling components.
Dyeing is effected by heating the fabric in a solution of an organic compound, typically a nitrophenol derivative, and sulfide or polysulfide.
The organic compound reacts with the sulfide source to form dark colors that adhere to the fabric.
A distinction is drawn between dyes that are meant to be used on cells that have been removed from the organism prior to study (supravital staining) and dyes that are used within a living body - administered by injection or other means (intravital staining) - as the latter is (for instance) subject to higher safety standards, and must typically be a chemical known to avoid causing adverse effects on any biochemistry (until cleared from the tissue), not just to the tissue being studied, or in the short term.
