Formulation of artist's oil paints, color science, and metamerism.

Factual Questions
1

Are artist’s oil paints, the expensive little tubes that come in dozens of different colors, formulated with different unique pigments? For example, historically, colors like “cobalt blue” and “vermillion” and “chromium yellow” were actually the distinctive colors of specific chemical compounds, and at least some of the paints with those names were pigmented with those specific compounds. Would that be the case if I went to an art supply store and bought a bunch of tubes?

Or, are they nowadays often formulated by mixing a small number of base pigments, like the housepaint they prepare on that machine with 8 or so pigment sources that are adjusted by a chart and then added to a white base?

I want to use artist’s paints as a tidy example of things whose reflection spectra are each distinct. So, I think if I visually match one color by mixing several other colors, and then compare the reflection spectra of these two, there will be differences. I also think that if I do that using sunlight illumination, the two I have created will be metamers and some other kind of illumination will make them look visually different from another.

Anyone know? Thanks!

2

I found this on the Winsor & Newton website. It says they use single pigments whenever possible. Here is a chart showing the composition of all of their oil paints. Quite a few of them seem to have just one type of pigment.

I don’t really know anything about chemistry, but it’s a place to start.

3

Wow, no wonder they call you “sapiens”. EXCELLENT lead, thank you!

This is exactly what I wanted to knowl. I anticipated that single pigment spectra would be especially important for greens and purples, but am pretty surprised to hear that about oranges. I got the chart with the chemical composition of the pigments, and it’s exactly on target.

“Single pigment” is what this little project is all about, and clearly Winsor & Newton have long appreciated the issues surrounding single pigments and spectra.

So, I see the same story pretty much applies to acrylics. I figured I needed oil paints because I remember seeing big selections of them for sale in expensive little tubes with pigment names on them. The fact that this is also true of acrylics means that I don’t know which of these two to use. Maybe I should prefer acrylics because they dry faster? Or what other reasons do I have to pick one or the other?

In my project I want to create splotches of single paints on a white background. I don’t need to mix them or paint them over one another. I do, though, want to be able to get them sort of faint in some cases, by having poor coverage, like strokes with a brush that is not so full and not held so directly against the substrate.

How does working with acrylics compare with working with oils???

Thanks!

PS - if it had occurred to me to look for a manufacturer’s web site, I would have looked for “Windsor & Newton” with a “d”, and figured they weren’t web-ready if I didn’t find it!

4

Google would have been smarter than you - I’m guessing it’s a common error. (I know of them, but I’m no painter.)

5

Paging OpalCat!

I’m not much of a painter (mostly watercolors) but I think acrylic is a lot easier to use. You can clean up with water and it dries a lot faster. You can buy a big set of acrylics for pretty cheap. How much area do you have to cover? Both acrylics and oils are fairly opaque. I’ve never tried thinning acrylics with water for a translucent effect. Can you just mix it with white to mimic the effect? Can you combine it with water colors for the “faint” effect?

6

If you’re painting big areas of solid color, I would recommend acrylics. Although oil can do the same thing.

Do not use water to thin acrylics, though. Use proper extender, such as gel medium, or better yet (for your intended use) glazing medium, which includes a slow-dry agent. If you use tape to mask off areas, pull it up before the paint

Those big sets of cheap acrylic will be made from mixes of the cheapest available pigments, not single pigments unless it’s black, white, or brown. Golden Artist Colors makes the highest quality acrylics. One especially nice thing about Golden is that they have a sample of the paint from the tube painted on the outside of the tube over black and white bars, so you can see the sheen and transparency of the paint inside.

7

>Can you just mix it with white to mimic the effect? Can you combine it with water colors for the “faint” effect?
Ah, well, I can’t if this does what it is supposed to. I want to paint splotches of, shall we say, “pure pigment color”. Then, I want to take monochrome digital photos of the whole thing, several photos without moving anything, but use a different wavelength of light for illumination in each photo. Next, I want to create a dataset in which each pixel location is a variable (so there’s 32,768 variables, which happens to be the largest number of variables my software can handle), and each brightness corresponding to an illumination wavelength for that pixel is an observation. And I want to do principle component analysis on these, to create eigenimages, and then cluster analysis on the eigenvectors. If it does what I think it will, then all the pixels for a given paint, even if it’s splotched in multiple places and looks to the eye like another paint, will be assigned to the same cluster, and there will be a one to one correspondence between cluster and paint.

So I think this method should be able to see more than the eye. And, an “effect” that passes our inspection wouldn’t fool this method.

As far as area to cover, as long as I can take nice pictures of my “painting”, this will work. I think the smallest tube they sell of any kind of paint would be more than I need. I actually think I could make this work with dots on a microscope slide, but what I was picturing was more like a square foot of white with 10 or 20 or 30 splotches on it.

Thanks for all the input. I do think that acrylics would be more convenient.

If you use paint from a single tube, that is, without mixing, and spread it around so it covers the backing, how uniform does the color look? I think there are two issues - I know the paint has some kind of covering ability depending on how opaque it is, and I see there are ratings of each paint to describe this characteristic. So, I know that a paint that has poor ability to hide whatever it is on will also not look very uniform unless you can brush perfectly. I’m also wondering if oil or acrylic paints have any tendency to create variable color in a single paint. For example, sometimes if you mix lots of dish soap with water, and stir it in a glass, it never looks uniform. It looks like liquid crystal patterns, all ripply. Or, there are some artistic mediums that have dyes and pigments both, and depending on how you brush or stir them the pigments contribute more or less relative to the dyes, because the dyes are truly in solution whereas the pigment is separate particles that can be stirred up or settle or can get randomized or get aligned in some direction. Not sure if I am asking an intelligible question, but - any comments on this?

8

The paint direct from the tube covers the back color well, unless you scrap it thin. Oils will take days to weeks to dry. Acrylics will be a better choice for you I’d say. Remember that paint surface texture will result in the light scattering differently, so the less texture you have the better for what you’re trying I think. I haven’t painted in so long that I can’t give you any other advice. Opalcat or one of the others that currently paint, likely can help a lot more. You might even try a private message to her or one of the others. Do a search for critique this painting and a few members actively painting will come up.

9

Definitely acrylics - they’re cheaper and dry quicker. I’d recommend masonite or somesuch rather than apper or canvas, as you’ll want the most uniform surface for comparisons.
W&N (Artist, not Student) are good, and I use Daler & Rowney too - the A-series.

10

>Remember that paint surface texture will result in the light scattering differently, so the less texture you have the better for what you’re trying I think.

An interesting point. I wonder if I should paint it on glass, and then put paper or white paint over it, and then both illuminate and photograph it from the other side? I could have very heavy paint with a perfectly flat and uniformly glossy surface that way. Not that I need it glossy, specifically - but it’d be uniform, even from paint to paint.
In any case, I think I’ll go with your recommendation for Acrylic. Do you think the big crafts stores or the one fancy little artist supply place in the next county would have most or all of the Acrylic Artist line in stock? Or if I want that much choice should I shop online? I think it would be helpful to get some colors that look very similar to the eye, as part of testing this whole approach, so I guess it would be a big plus to look at tubes with paint dabs or even color imitations on the outside, rather than looking at any color chart on a computer monitor.
Artists must deal with this limitation all the time - do they buy all their paints from walk-in stores, at least until they know what a specific product looks like?

>W&N (Artist, not Student) are good, and I use Daler & Rowney too - the A-series.

Thanks. I saw from the W&N website that the Artist lines of both acrylic and oil are mostly single-pigment products, and as I think about it the reasons they care and the reasons I care are very closely related. The reasons are actually the same, if stated right.

11

Paints are pretty well blended already, so it’s usually not an issue, once you get it to the canvas, though, slight variations can occur. This is another reason to use a glazing medium, it is designed to aid in creating large areas of solid color. Use a big, soft brush with long strokes and variations should be minimized. Gessoed Masonite, in my experience, would be a good support to paint on for your purpose, it’s hard, flat, and smooth.

When a dye is used in paint, they use it to dye an inert, colorless pigment, then use that as the paint’s pigment. This is called a “lake” color, so when you see something like “Scarlet Lake,” that’s what it means. I don’t recall ever seeing an acrylic lake color.

I used to work in an art supply store, so I know exactly what I want, but I still go into the store so I can see the paint. Even a single-pigment color will vary from tube to tube, particularly the more transparent ones. The “fancy little artist supply place” stands a better chance of having good acrylics. Most manufacturers’ website have a way to search for retail distributors. Taking a guess at your location, here’s a list of places in Maryland that carry Golden.

12

Thanks, garygnu. Actually, some of those store locations would work for me. Also, I didn’t know that’s what “lake” meant. Interesting.

What do you think of painting on the back surface of glass? Do you think the appearance would be very different? It would probably produce a more uniform appearance, right?

13

Glass is a very difficult thing to get paint to stick to. If it’s thick enough, you can literally peel acrylic paint off glass. In any kind of normal artistic endeavor, I would say don’t paint on glass, but in your case it might be worth a try. I would be concerned about air bubbles disrupting the evenness of the paint.

If the store you go to has a frame shop,* ask them for a small piece of regular glass and a small piece of non-glare glass. Do a test with both and see how it looks. There are two types of non-glare glass, one with microscopic scoring on one side, and one with microscopic bubbles throughout the glass. Either will work, but paint on the fuzzy side if you get the single-sided version.

On a side note, since your purpose is rather scientific, I highly recommend picking up Blue and Yelow Don’t Make Green by Michael Wilcox. Your local library should have it. It’s not perfect, but in true Doper fashion, it uses science to decipher paints and color. I like his other book, The Artist’s Guide to Selecting Colors, much more, but it is harder to find. IMHO, both should be required reading for both artists and art supply store employees.

14

Thanks!! And may I recommend Principles of Color Technology by Billmeyer & Saltzman - it’s not aimed at artists, and is somewhat mathematical, but thoroughly enjoyable. Plus, they have strongly metameric color chips glued inside the front.