What is the difference between a pigment and a dye ? And why does it matter !
Colors come either from dyes or pigments. Both dyes and pigments are colored because they absorb only some wavelengths of visible light. Therefore theoretically a dye and a pigment can give the exact same color impression to our eyes ; the key difference lies elsewhere.
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution where it is completely absorbed. That means it has formed a compound with the solvent molecules to create new « colored » hybrid molecules.
Think industrial mint syrup in a glass of water : the sugar and green coloring agent (organic mint leaves aren’t bright green!) of the syrup have completely disappeared.
Dye solutions are usually the go-to strategy for inks and markers.
On the other hand, pigments cannot be absorbed by any solvents or substrates. They are stable, stand alone molecules, most of the time in a powdery form. In order to use them as coloring agents, one needs to set them into a substrate where they will be suspended and, ideally, stabilized in that state.
Think oil and vinegar salad dressing : shake it well and you get the impression it is one liquid element. Let it sit for a while and two different parts appear. The oils droplets are only suspended in the water-based vinegar part and will eventually regroup.
Colored pigments are most commonly used in oil paintings, watercolors or acrylic.
As an artist, knowing that difference will help you better use your materials to get even more awesome results. As a conservator, it will help you identify weaknesses and probable deterioration causes and act upon it.
Pigments are stable and more or less keep their colors whatever happens. Their substrate however is usually the weakest link : lose the support and there goes your color, back to its original dust form and sticking to a yellowing varnish instead or, worse, ending in a darkening concoction created by a mad genius.
Dyes are chemically bond to the material : whatever affects it will affect the color and its shade. Sunlight of the curtains for too long ? Bye bye sweet pink and hello grayness. Worst case scenario : the very nature of the dye will literally eat at the material it is with.
Now for a trick question : according to you, what are tattoos inks composed of ?
Answer is this way.