A Yellow Paint Experiment | Lake pigment from thyme

Back when I made my very first set of paints, I had a really nice yellow. I’d made several yellows from various plants and did lightfast tests on them. All failed except for the one, gorgeous yellow. Not only did it pass, the yellow color actually intensified with the light exposure. At that time, I wasn’t keeping records of how I’d made the paints, but was just blindly experimenting. I ended up with a good bit of that yellow paint, but over the years since, I used it all. And over the years since, I’ve tried to reproduce that color. Nothing worked, and I’d about given up hope. But today I did another yellow paint experiment and there’s a glimmer of hopefulness so far!

Another Case of Mistaken Identity

And this too, has to do with sassafras trees. The other mistake was mistaken identity of tree roots. I thought it was sassafras, but in fact it was Osage. There wasn’t much to go on except part of the trunk and the roots. And I’d guessed wrong. But the root bark gave me a very nice orange lake pigment anyway. This yellow paint I’m trying to reproduce has led to another mistaken identity. I used store-bought gumbo filé to make the first paint. Well, it’s sassafras leaves that filé is supposed to be made from. I’m half Cajun, so I wasn’t wondering what the spice was made with. I didn’t read the label.

As it turns out, that filé also had thyme leaves in it. I did not know that gumbo filé had thyme in it, too. I found that out by actually looking at the label recently, hahahaha.

The Kind of Yellow Paint I’m Hoping For

What I want is a brilliant, richly pigmented LIGHTFAST yellow. I know that’s a bit much to ask for in a handmade paint, but it’s what I want. Since the rocks are all opaque and earthy tones of yellow, with a lot of brown, that’s not the answer. Plants often give much brighter color, but the color is fleeting and fades or oxidizes. Sometimes that change happens quickly, like overnight, and sometimes it takes weeks. Rarely, a plant pigment offers stability enough to be useful.

Organometallic Molecules

I can find very precious little information online about the pigment molecules in thyme. However, wool and fabric dyers have known a secret that I believe offers some insight about why certain plants do offer color that is lightfast when others do not. Dyers use a mordant to make the color stay better on the fibers. The mordant creates molecules with a combination of organic and metallic/inorganic parts. When the bond is tight between the two, the color is fast. When the bond is easily broken down by oxidation or UV light, or ionized with water, then the color fades.

In the case of the blue I use for watercolor sometimes, the molecule contains iron and magnesium. But the bond is easily broken if anything else is added to the juice of the dayflower petals, and the color turns gray. If I use the juice alone, to transfer to the paper as a stain, then the color is fast for years. I think something similar is going on with the pigment in thyme. I am putting on my scientist hat to hypothesize that my yellow paint made from thyme will be more stable and longer lasting because of an organometallic pigment molecule featuring aluminum.

I did learn that the pigment compounds in thyme are very similar to those in weld, an ancient plant used for a very long time to make a lightfast yellow. They’re called lutein and zeaxanthin. I believe it is the zeaxanthin responsible for the yellow intensifying when it’s exposed to sunlight. Here’s a research paper with a lot more information: https://www.mdpi.com/2571-9408/4/1/26

Are You A Chemist?

If you are, I would love to know if you have information on this topic. My knowledge of chemistry is specific to the fields I worked in, which did not have a thing to do with art or making paint. And even though I’ve had a fair amount of chemistry classes, it has been so long since college, that I’ve forgotten most of what I had learned.

I found one article discussing the pigments in thyme in context to the antimicrobial properties, but if you’re interested in the chemistry of it, then it can offer some insight. The difference between the thyme color and the dayflower blue color is that it isn’t bothered by the heat of extracting it in water, and sunlight only intensifies the color. Adding the dried lake pigment to oil to make the paint did not change the color, either. The article I mentioned above focuses on a different species of thyme, but it did mention that aluminum is the metallic inorganic element that caused the pigment to be most lightfast (iron can also be used). Using alum in my laking process gives the aluminum to the pigment molecule.

Making Yellow Paint by ‘Laking’

To make a lake pigment is to perform chemistry to bring about a chemical reaction. It’s not necessary to understand the chemistry part of it, if you don’t care to know it. But it helps to know what you want to happen and why certain things can bring that reaction about.

My experiment with the yellow paint is not to understand the ‘why’ behind the color so much as it is to know the answer as to whether or not it will withstand the test of time.

The ingredients I’ll use to make this lake pigment is alum (potassium aluminum sulfate), calcium carbonate, and a filtered water extract of thyme. Later I will try the same process using iron sulfate, as this supposedly might make a green shade instead of yellow. But that’s a different experiment for a different day. First, the yellow.

Less Reactive

When I make a lake pigment, there is less drama in the mixture than what I’ve seen in videos online for how to make them. I more interested in causing a flocculation than a volcano-like reaction of expanding foam. In the end, it is causing the pigment molecules to bind together with an inorganic component. And this makes the color settle to the bottom or rise to the top, which can then be washed and filtered.

And so the object is to cause the color to ‘flock together’ and either rise or settle so I can pour off the remaining liquid and then filter out the particles that are left behind. One of my first jobs was in the lab of a water plant. The operators cleaned the water by ‘floccing’, which is similar to the method I’ll use to gather the pigment particles. In the water plant, the intention was to gather up the impurities and cause them to settle so that they could then filter the water without the solids.

The Process

Here’s the steps I took in this first experiment. It’s only been a few days since I made the first tiny batch, and so far the color is good and the results are promising. In a little while I’ll gather some fresh thyme and try a larger batch. When I do that, I’ll make a video of the process and show the whole thing. I’ll post the video here, and also make a new blog post about it. Periodically, I’ll update to say how the samples are doing in the sunlight exposure.

Videos

I’m repeating the process and trying to remember to video what I’m doing. In order to not have to upload very large files, I’m breaking it into parts. As I get them made and edited, I’ll upload them in parts. Part 1 & 2 are up now:

• Part 1 shows harvesting and bundling the thyme for drying.
  • https://youtu.be/Hr-_q8rZn6E (the one above)
• Part 2 shows stripping the leaves and making the extract
  • https://youtu.be/GjXjjaTTxdE
• Part 3 shows how I precipitated the pigment
  • https://youtu.be/ksy_22ccwmo
• Part 4 shows how I make an oil paint with it (that’s this video)
  • https://youtu.be/I0dwqcm0kDs
• Part 5 shows me using it on a painting (it will be a while before I make this one)