One of the biggest hurdles that new artists come across (particularly in the watercolour community), is that there is a surprising amount of technical information. Whether it’s pigment numbers, lightfastness, or various other properties, picking the best art materials is often not as simple as just choosing a colour you like.
On product packaging or in discussions among artists, you may have heard the terms “pigments”, “dyes” and “lakes” to describe the colourful stuff in our art materials. In this post, I will explain the difference between these three categories and what each is used for. What makes them different? Why are dyes rarely used in professional paints? Why should you care? Understanding the difference between different types of colours will help you make informed decisions about the best materials for your practice.
Pigments are composed of one or more chemical compounds that have a distinct colour. These usually consist of larger molecules that cannot be dissolved in common art mediums (i.e. water, oil, alcohol, or acrylic) . Because they are insoluble, in order to turn pigments into paint, they are suspended in their respective binder, which coats the pigment and allows them to adhere to the surface you are painting on.
If you look closely enough at pigment-based paints (some will require a magnifying glass or microscope), you can see what appears to be individual particles sitting separately – even with phthalo or quinacrhttps://khannahshoneyhues.com/wp-content/uploads/2022/11/Handmade-Kid-Shop-Costumes-archive-1.jpge pigments! These are actually small groupings of molecules bound by strong intermolecular bonds and are 0.05-0.2 micrometers (or 50-200 nm). All of the most common professional paints are made from pigments; cobalts, cadmiums, ultramarines, quinacrhttps://khannahshoneyhues.com/wp-content/uploads/2022/11/Handmade-Kid-Shop-Costumes-archive-1.jpges, phthalo.
The fact that pigments are insoluble should not be confused with how easy it is for them to mix with the binder; cobalt and phthalos are both insoluble, however phthalo compounds are also hydroscopic, and therefore are more resistant to being mixed into a paint.
Dyes are coloured substances that chemically bond to the substrate (paper, etc) they are applied to. Unlike pigments, dyes are often soluble – especially in water-based mediums. Dyes can be both natural-based (from plants, roots, and veggies), and artificially synthesised, however whilst pigments have lots of intramolecular bonding between molecules, dye pigments exist in the solid and solution states as single molecules, with particle sizes of 1.5-4 nm (a million times smaller than a mm!).
Another difference is that whilst pigments require a binder to attach to a substrate (paper, canvas etc), dyes are more likely to chemically bond to the substrate without additional help. A Caveat is that for some dyes, a mordent is needed to help them to bind (see below).
However, dyes often have very poor lightfastness. Smaller particles have a larger surface area compared to their size, and so there are more surfaces exposed to direct light/UV radiation.
However dyes do have some advantages. Dyes have a greater transparency than pigments – again, related to the pigment size. Colour payout is also much greater (at least in the short term!), as the particles do not refract light well. Think of it like a quinacrhttps://khannahshoneyhues.com/wp-content/uploads/2022/11/Handmade-Kid-Shop-Costumes-archive-1.jpge vs a cadmium – the latter is more opaque, as the particles are larger. This is why many alcohol markers and inks use dyes in their colour formulations.
Wikipedia defines the composition of a lake pigment as a “dye precipitated with an inert binder” – these are usually metallic salts, for example chromium or cobalt, however way back when chalk was also used. For context: a metal salt is composed of a metal ‘cation’ (i.e. has a positive charge’), plus an organic or inorganic anion (negative charge species). For example, table salt is made up of sodium (metal cation), and chlroide anions.
The binders that are used with the dyes are usually colourless, and must be chemically neutral and insoluble in the binder, however must also precipitate the dye (cause the dye to fall out of solution, and exist in a particulate form similar to pigments).
Unsurprisingly, as these pigments are derived from dyes, they often have low lightfastness. There are a few brands that still use ‘lake’ in their paint names, for example Sennelier, and Old Holland. In many cases this is not in reference to lake pigments, but a bastardization of the french lacque, which is used to describe any transparent pigment. The best way to check whether this is the case is to look at the pigments in the paint (usually referenced on the back of the tube), and to look them up.
Which should I choose?
Well, this all depends on what you’re doing, and what will happen to your piece of work. If you’re going to keep your art in a journal, and rarely look at it, it honestly doesn’t matter which of the above you use. Likewise, the allure of colour change over time might work well for more abstract artworks.
However, a general trend amongst artists has been to solely use ASTM I-II rated pigments. ASTM stands for the American Standard Test Measurement, where I is excellent and indicates a paint won’t fade in 100 years in ambient light, whereas a rating of V indicates a colour will fade or change in under 20 years.
Thank you for joining me in this journey; I’ll see you next time!