Colour Technology

How colour is manufactured: pigments, dyes, lakes and inks; opacity and tinting strength; lightfastness; effect and interference pigments; colour that changes with heat, light or voltage; and what happens to colourants when material is recycled.

Explains principles and history. No formulation, synthesis or handling instructions are given.

19 topics · 76 evidence-labelled claims · 64 sources

Colourants

Pigments, dyes, lakes and inks.

What is the difference between a pigment and a dye?A dye dissolves in the material it colours, or in the liquid that carries it, and ends up as single molecules bound to or dispers…What is a lake pigment, and why do so many of them fade?A lake is a dye turned into a pigment by precipitating it as an insoluble compound, usually with a metal salt and often onto a co…How do offset, flexo and inkjet inks differ, and why do some prints fade faster?Every ink is a colourant carried in a vehicle, but each printing process needs a very different vehicle: offset uses a stiff past…How does the binder change the colour of a paint?The binder is the film-forming material that holds pigment particles — linseed oil, egg yolk, gum arabic, acrylic polymer — and i…Why is titanium dioxide the white pigment in almost everything?Because its refractive index — about 2.What is carbon black, and why does a tiny amount grey a white so much?Carbon black is almost pure elemental carbon made by controlled incomplete combustion or thermal decomposition of hydrocarbons, f…

Performance

Opacity, tint strength and lightfastness.

Why do some paint colours need three coats to cover while others hide in one?A paint hides a surface when light entering the film is scattered back out or absorbed before it reaches what is underneath and r…What is tinting strength, and why do some colours overpower a mix?Tinting strength is how much a colourant changes a white (or another colour) per unit added.How does pigment particle size change colour, and what does 'dispersion' mean?Particle size sets how a pigment scatters light: particles far smaller than a wavelength scatter weakly, so the pigment looks tra…What do lightfastness ratings like Blue Wool 7 or ASTM I actually mean?They are ranks, not lifetimes.

Effect and smart colour

Metallic, pearlescent, structural and chromic.

How do metallic and pearlescent pigments work, and why do they change with viewing angle?Both are platelet pigments that work only when the flakes lie flat, parallel to the surface.How can a colourless material make colour by interference, and why does it shift with angle?A transparent layer a few hundred nanometres thick reflects light from both its top and bottom surfaces; the two reflections add…How do fluorescent colours and optical brighteners make things look brighter than white?A fluorescent colourant absorbs light at one wavelength and re-emits part of it at a longer one.How do glow-in-the-dark pigments work, and why are most of them green?A phosphorescent pigment stores some of the energy of the light it absorbs and releases it slowly as light after the source is re…How do colour-changing materials like thermochromic ink, photochromic lenses and smart glass work?Each switches between two optical states in response to a trigger.

Colourants and recycling

Masterbatch, de-inking, residual colour and repigmentation.

Which colourants survive recycling and which can be removed?Colourants built into the material — oxides dissolved in glass, pigments dispersed in a plastic melt, dyes fixed in fibre — survi…How is ink removed from recycled paper, and how is deinkability measured?Recovered paper is pulped in alkaline water to loosen the ink, then ink particles are removed mainly by flotation — air bubbles c…Can recycled material be made white again?Sometimes, by one of three routes: hide the base colour under enough white pigment, remove the colour chemically (bleaching pulp,…How is recycled plastic recoloured, and why is it harder than colouring virgin plastic?Recycled plastic is recoloured the same way as virgin — usually by blending in a concentrated colour masterbatch during moulding…