How to Prepare a Pigment Dispersion With a Rock Tumbler
Why I Create Pigment Dispersions
Artist paints absolutely thrill me with their colors and brilliance. With so many different types of pigments—some warm, some cold—it’s hard to choose. To have a decent color selection, I have to buy smaller portions, because artist paints are usually quite expensive unless there is a sale.
Then, not so long ago, I began to find numerous vendors of dry and dispersed pigments. I automatically realized the potential for savings in that I knew a 2 ounce bottle of dispersed liquid pigment could make a pound or more of artist-grade acrylic (with acrylic medium, of course). Obviously, dry pigments are even more concentrated and would produce much more paint. But dry pigments, in most cases, are quite difficult to get into smooth paints. They require mulling and mixing sometimes additives need to be included to help disperse the solid pigment into the medium.
After many months of online digging and contemplation, I came up with a workable solution. I would buy a decent quality rock tumbler that would not leak, some ceramic tumbling media, and a few non-hazardous chemicals—and set straight to work. Believe it or not, all materials and equipment were procured from either Amazon or eBay.
Don’t be alarmed, but it does take a few ingredients to get started (along with the rock tumbler). Most of these ingredients are easily found online. Also, the initial investment might seem much, but you’ll use so little of each ingredient in each go that it’s certainly worth it. All the ingredients, besides the dry pigment, are liquids and soluble in each other. They are as follows in order of importance:
- Distilled water
- Polyethylene Glycol 300 or 400
- Nonylphenol Polyethoxylate or Triton X-100 (surfactants)
- Polysorbate 80 (surfactant and emulsifier)
- Silicone defoamer soltution
Personally, I’ve been using a defoamer liquid that is for spas, but as long as it is silicone-based with no other additives it will work. Online suppliers who sell cosmetic-making ingredients usually have some type of silicone defoame.
Purpose of Polysorbate 80 Surfactant
In my experimentation, I have noticed that Nonylphenol polyethoxylate mostly wet the solid pigments while the polysorbate 80 acted as an emulsifier keeping the pigment dispersion stable.
My early attempts at making dispersions where fairly successful but they quickly separate into a solid and liquid phase. Still functional yet requires constant agitation to be useful. At that time I was using very little polysorbate 80. Now, I use 1 part Nonylphenol Polyethoxylate to every part polysorbate 80. So far, my dispersions are lot more stable. The recipe examples I posted have these new amounts noted.
Wetting and Dispersion of Solid Pigments
The three main key ingredients are the PEG 300 (polyethylene glycol 300), the Nonyl Phenol ethoxylate, and the polysorbate 80.
These liquids will wet out and make dispersion of solid pigments into a liquid form easier. Some organic pigments like the phthalo blues and greens, carbon black, and Van Dyke brown may pose a challenge to disperse.
Usually the nonyl phenol ethoxylate and polysorbate 80 combined would represent 16 to 20% of the total mass of the dispersion. But with the tougher to disperse pigments, they might need to be adjusted to as much as 22 to 26% total by weight. The addition of up to 5% glycerin may be required. PEG 300 or 400 usually is 8% by total weight regardles.
Pigment dispersion in rock tumbler
Video: Running Pigment Batch in Rock Tumbler
The Rock Tumbler
The biggest expenditure of this endeavor will be the rock tumbler. I use the because the 1.5 pound capacity barrels are the right size for what I am doing with the pigments. Lortone triple barrel rock tumbler
This tumbler runs quietly and the drums never leak as long I am careful to secure the lid properly. It is imperative that you use a good quality rock tumbler that has barrels that are leak-proof. Pigments, especially the organic ones, will make a horrendous mess if they leak out! Do not waste your money and time with the plastic toy rock tumblers!
Summary of the Process
- First the pigment is weighed into the empty drum.
- All liquids are measured accurately and blended in a suitable glass container. I use student-grade lab beakers.
- Liquid mix is stirred thoroughly until a uniform clear liquid with a yellow tint result.
- Then the liquid mixture is added to the dry pigment.
- Add no more than 1% defoamer to mix.
- Next up to one pound of ceramic tumbling media is added but BE SURE DRUM IS NOT MORE THAN 2/3 FULL! Otherwise adequate mixing will not occur.
- Then pro seal the drum and place on the tumbler and connect to 120 volt AC source. Run a minimum of 24 hours. For difficult pigment, 48 hours may be best.
Recipe #1: Pigment Yellow 74
Pigment Yellow 74, also callled hansa yellow or Dalamar yellow, is mid-range yellow with a slight green tinge. It is a good primary yellow to have. To prepare this dispersion you will need:
- Pigment Yellow 74 (96 grams)
- Nonyl Phenol ethoxylate (8 grams)
- Polysorbate 80 (8 grams)
- PEG 300 (16 grams)
- Distilled water (36 grams)
- Silicone defoamer (1 gram)
First add dry pigment to rock tumbler drum then one pound of ceramic media. Next seal drum shut and check that it will not leak. Then tumble for 24 to 48 hour.
Recipe #2: Pigment Green 36
Pigment Green 7, also known as phthalo green blue shade, is an intense copper-based emerald green organic pigment. This green makes brilliant, almost neon light greens with the hansa yellow series (see above) as well a wide variety of aquas, teals and turquoise with phthalo blues. To prepare this dispersion you will need:
- Pigment Green 36 (90 grams)
- Distilled water (108 grams)
- Nonyl Phenol Polyethoxylate (13 grams)
- Polysorbate 80 (13 grams)
- PEG 300 (16 grams)
- Glycerine (10 grams)
- Silicone defoamer (1 gram)
Add pigment first to empty drum. Mix all liquid components completely then add to pigment in drum. Add as much ceramic media as possible until the drum is 2/3 thirds full but no more! If you can get 1 pound of ceramic media in there then go for it.
Important Role of Polysorbate 80
My experimentation has shown that the polysorbate 80 is the emulsifier Or stabilizer for the dispersion. The NonylPhenol ethoxylate mainly for wetting. In my early attempts, I used very little polysorbate and my mix would separate often.