Tuesday, January 11, 2011

Confused about artists' materials? 1. A very short and easy technical history of oil paint

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Have you ever wondered what goes into artist grade paint? If you've ever shopped for artist's oils or acrylics you may have noticed that there's a lot of information surrounding those little tubes. Even right in the store, the paint displays are full of ratings, claims and data to take in. Dig a little deeper; look into articles and books for artists, and you'll find advice on how the individual colors behave, information describing good and not-so-good ways to use the media that mix with the paint, and lots of factoids and explanations about why this is so.

Does all of this information seem confusing? Sometimes contradictory? As if it points everywhere except towards the solid answers you need? If you've found yourself confused trying to make sense out of everything you've read, heard and been told about artists' paint, it may be because a lot of the information out there is out of date, or extrapolated from materials that don't behave like your paint, or simply well-worn paint mythology. Your confusion is not a lack of insight or knowledge; in fact it's a sign of a solid scientific intuition and curiosity taking hold.



So let's talk about paint, and find some simple and general scientific principles that will help sort the fact from the noise, and identify the areas where we really do need more data - the open questions we need to ask as users of these materials.

Let's start with a short overview of oil paint.

Oil paint: A long time ago oil paint was used far less frequently for painting than it is today. The paint was also very different from the oil paint we use today, right up to the time of the Impressionists. Paint was prepared by mixing pigment with oil, and a number of different oils were used. Not all of them worked very well for long-lived paintings, and many of the pigments were also short-lived. Reporting on what worked and what did not was scattered and inconsistent. Some of the oils reacted chemically with some of the pigments, Some of the pigments reacted chemically with some of the other pigments, and the paint itself was very liquid and unstable. There were actually two ways the paints were unstable: the long term chemical instability of negative paint and pigment chemical reactions, and the short term instability of pigment refusing to stay mixed with the paint in a usable oily liquid form.

Then two big paint technology advances happened. At around the time of the Impressionists, reformulations were developed for oil paint using additives to the pigment and oil mixture. The paint became thicker, easier to pack and carry, and the pigment remained mixed up well with the oil. The new formulations remained nice and paste-like and usable as long as they were kept from air. Short term stability problem solved!

The other big paint technology advance was the chemical revolution, which started late in the 19th Century and continued into the mid 20th Century. For the first time, people really began to understand why some things would react in a systematic and predictive way. A predictive understanding involves taking what you know from observations , comparing it to a model for "how things work in general", and then having the ability to extrapolate how something brand new could work. With a better understanding of chemistry, more chemicals began to be produced. This included new synthetic pigments and synthetic analogues of natural pigments. Paint systems - full ranges of color from pigments that would not chemically react - were also developed.


So why the confusion?
We know where oil paint started out, we know where it is now, and we know what happened in between. It seems like a staightforward picture, so where is the confusion and contradiction coming from? And how do we get to the science? If someone, say a very nerdly painter, wanted to find out more about the chemistry and physics of oil paint, the peer-reviewed scientific literature on oil paint and oil paint's components is the place to start. And that's exactly what this nerdly painter decided to do.

The majority of the research articles available on artists' paint or on the behavior of a paint component studied inside the chemical environment of artists paint seem to come from the Conservation community. Conservation scientists are typically very good chemists with a very good understanding of the Art they study as well. However, they encounter and study old paintings. When painters and people compiling information on paint look to the conservation literature for information on the properties of paint they discover ... the properties of very old paint. That very old paint is chemically and physically a very different beast from the paint we use today.

The other source of data on modern paint formulations is the industry that makes the paint. Paint companies do provide data on their pigments, the properties of their media, and their processing methods used to turn all of those ingredients into paint. A good chunk of their processes and formulas don't seem to make it into the literature (hey - if you disagree, help me find these articles!!). There are some good facts offered up by the paint companies. Without the information sharing and cross checking that happens in the peer reviewed literature it's difficult to connect up all the facts.


How do we cut through the confusion?

OK. So we know a bit about oil paint, we know that there is a good amount known scientifically about old paint formulas, but the formulas have changed significantly. There's also some information on modern paint offered up by artists' paint companies, but we need to connect those dots. Where do we go from here? What data re available to help us cut through the confusion?

There is a huge amount of research and data on the various molecules that make up oil and acrylic paints, but most of it is targeted towards other industries where these molecules sit in mixtures and formulations with very different chemical and physical properties. Some of this data will be useful in understanding modern oil paint and modern acrylic paint. We're not going to go there just yet. We'll need to look at each piece of data and understand what it means for artist paint. That involves a bit of additional science here and there. In the interest of not firehosing readers with too much technical information all at once, it seems best to proceed datum by datum in separate posts.


Next up: Viscosity, why does it matter?

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