Archive for December, 2010

Pigment categories – the blurry lines

December 26, 2010

It’s hard for me to believe that I’ve let my blog go for five whole weeks. I never thought I’d be one of those authors who had to post “Sorry it’s been so long since my last post” – and yet, here I am. Sorry, folks. It’s been a tough month. I’m abandoning for this post, and maybe the next post or two, the discussion of classical underpainting techniques; but I am continuing to research and experiment, faithful reader, and I’ll return to the topic soon.

Back to art materials philosophy. Some time back I listed some basic definitions for the four categories of artist’s pigments: natural inorganic, natural organic, synthetic inorganic, and synthetic organic. (See the posts here, here and here.) The categories seem straightforward enough once you become familiar with them. However, things can get a bit weird if you start trying to nail down certain pigments.

Take Prussian blue, which is considered a synthetic inorganic pigment, in fact the first modern synthetic pigment. This is a pigment discovered accidentally in the early eighteenth century while attempting to create a carmine lake pigment with what turned out to be some tainted substances. What happened was that some potash contaminated with animal blood was used to precipitate the iron-based lake pigment, accidentally forming iron ferrocyanine, which makes a powerful blue. (Lucky accident!) So, but here’s the question: how is it that when a natural organic lake pigment received an additional natural organic element, it turned into something that is considered a synthetic inorganic? Weird – why is this pigment not considered a natural organic, like the carmine lake? I suppose it’s because in Prussian blue there is no actual dye involved – but still, it seems arbitrary.

A lake pigment is generally thought of as a dye precipitated onto a base of alum; but as indicated above, not all lake pigments are based on alum. They can be based on iron or copper instead, or even other metal salts such as chrome or zinc. Sometimes, even when a natural dye is used, these lakes based on other metals are viewed as synthetic, or semi-synthetic, rather than natural. Why? Why is a natural dye laked onto alum considered a natural pigment, but the same natural dye laked onto copper may not be? Alum is potassium aluminum sulfate, the copper mordant is copper sulfate pentahydrate. Both are metal sulfates, pretty similar stuff. A dyer would consider any dye obtained from natural sources to be a natural dye, regardless of what mordant were used to bind it to fabric, be it alum, iron, copper, tin, chrome or other, and I would agree – and I don’t really think of natural dyes laked onto different metal substrates as being categorically different from one another.

Precipitating copper blue

Precipitating copper blue

But I can easily get myself into more trouble. Green and blue pigments can be made from copper without the addition of a natural dye, and yellow and red pigments can be made from iron – and these are also considered to be synthetic pigments. But why? If laking a natural dye onto alum, iron or copper results in a natural pigment, then why does it become synthetic if I follow exactly the same procedure, but only leave out the organic ingredient?

It’s at this point that the whole question starts to break down. One person to whom I mentioned my interest in natural pigments immediately quipped, “Well, what’s natural”? At the time I confess I was a little irritated by such a flippant-sounding dismissal of what has been a passion for me – but now I see the wisdom in it, regardless of how it may have been intended. What is natural, anyway? Don’t get me wrong: the words “natural” and “artificial” are opposites with real definitions; but as soon as we start trying to identify categories, we have to start drawing lines, and that’s where things get messy. At some point you have to chalk it up to useless semantics and move on to another aspect of the discussion.

This is all a little illustration of why, though my original direction (years ago, now) was almost entirely about natural pigments, and though I still write about my love for colors from natural sources, I now pay little attention to such distinctions when considering my philosophy of materials, just as I now pay little attention to toxicity (other than as a necessary practical concern). Natural, synthetic, doesn’t really matter. What does matter, to me, is whether a particular art material is sustainable – meaning that I think we artists will pretty much never be forced to stop using it. That means no industrial processes required in that material’s production, no hydrocarbon feedstocks are used, no destruction of landbases necessary – and we aren’t dependent for our materials upon the needs of the giant automobile, plastics and textiles industries. In a perfect world, that would mean art materials that could be made locally, from regionally common materials, and without harming the ecolocality in any drastic way. The only pigments that are categorically excluded from my list are the synthetic organics; they are derived from hydrocarbons, and really can’t be considered sustainable no matter how they’re sliced. Also excluded would be any other pigments that absolutely require an industrial process for production. The ones that would not be excluded are the natural earths; the natural organic colors; and artificial pigments easily synthesized from common metals and minerals.

Yes, this is the kind of thing I spend my time thinking about. I think it’s important.

– L. Lawrence