collecting native minerals

[Anonymous]

I would say I am blessed with my location. I live at the foot of the Sierra Mountains in California. I have stumbled on places that hold great colors. My ochres come from a clay deposit near a hydraulic mining area. I get terrific grade yellows, reds, and browns. From another location I found a light yellow streaked chalk. Black shale offers a near black warm gray.

From some place I can't remember where, I found deep purple rocks. I throw hard stones, along with hard porcelain balls into rock tumblers. I just mulled the purple rock. It turned out to be a purple tinted very dark and rich brown. It is lovely. I figured it would be. I successfully used the same stone dust to glaze pottery in the past.

The quality of my colors are such, I don't need to buy many commercial minerals. I actually like the found material as well, or better.

I can control grinding with these colors. Hand grinding results in uneven crystals. It is my prejudice this lends life to the pigment.

Has anybody else any experience, positive or negative, with found colors?

Vince

[DLH]

Vince,

One of the reasons I love egg tempera is that I’m close to, and in control of the raw materials of painting. You have certainly gone me one better.

Do you paint representational or abstract? Do you tailor your subjects to your colors, or do you paint any subject with the colors you find? Do you supplement your palette with commercial pigments? What do you use for white?

Have you ever tried to make pastels with your colors?

Doug

[Anonymous]

Doug,

Are you Doug Tiller?

I would be a purist in this regard, if I could fill out my palette with found materials. I'm supplementing my natural palette with Titanium White, and some select reds, greens, and blues. I have a dull earth green, and a steely grey, that looks blue.

Actually, being a purist was my intention, when I collected this material fifteen years ago. I used my mineral colors to "paint" raw clay sculptures. It was born of an affair I had with Zen, and Japanese traditional pottery.

My prejudice towards self reliance in art materials is fueled by my experience with at mastering drawing with charcoal. I think I bought every available type of charcoal. I found the process cumbersome, and the result less than satisfactory. As a lark, I tried charcoal left behind in my fire place. I had been burning local brush. That charcoal can do it all.

I have just begun preparing to paint, using ET. My work over the last fifteen years has been of the very large, thus my monicker. The small is in my comfort zone, because I use to illustrate biology manuals.

My intention is to paint representational pictures. But, who knows?

The gallery here is thrilling. I adore many of the works on display.

Vince

[K. Lee]

Although I feel resource is one of the things a true artist, if that is a label, can hope to become, I'd be just a bit leary without knowing the components of a material. Perhaps it's not of import, but I'd assume for the worst anything could be made into paint, and also may have unpredictable results. If I come to the point where I process paint I'd be sure to check the chemistry carefully, even avoid colecting stones or areas where tree sprays, et cetera may have been applied (probably obscure today).

Of course if longevity is not of importance in the work (which it seems many artists working today are playing credo to in mixed mediums) almost anything could be organized into a paint. It truly is an underestimated capacity when looking at old masters how they made their paint, or how it was done.


Lee

[Anonymous]

All of the colors I have picked up have been out in the weather, and sun. Light fastness is not an issue. The clay field I happened on (I doubt it has been spotted by anyone else, as remote it is) is in a National Forest. Pesticides, or herbicides are not an issue. The rainbow of ochres are the usual clay based pigments. I do have a few colors sourced from more pure minerals gathered elsewhere, such as the "Purple Rock. " It contains a very high percentage of Manganese. I haven't been able to find a commercial equivalent.

I just ground two Umber specimens. They came from two localities. One is more pure Manganes/Iron mineral. It is more transparent, and a touch brighter than the ochre Umber. Their hue is identical.

[Salamander]

Hey, good work you're doomg there......keep it up!
Eric in Oceanside

[PhilS]

I think it's a great idea, Muralman,
Obviously, if the rocks have been sitting out in the sun for hundreds of years they are going to be lightfast. I would love to do a painting with pigments from my backyard...
Actually, I'm getting ready to start a portrait of my girlfriend holding one of her favorite chickens in her lap. I plan to do the painting using eggs laid by that chicken. Pigments, however, will have arrived in a UPS box from somewhere in California...
If you ever get a chance, I strongly recommend visiting a place called Roussillon, France. The soil everywhere around is composed of brilliant shades of ochres: yellow, orange, red. It will blow your mind.
Phil

[K. Lee]

Sounds excellent muralman, and PhilS, I'm jealous in a way. I'd love to have the abillity to prospect, saunter, and safely make paint that way. At the moment I'm trying to figure out a way to carve stone without making myself a personal nightmare.

Phil, I myself without a better chemical composite (knowing more about each element) would just be weary. My observation was probably more a structural one then about light-fastness, although that's a very valid observation I think. Stones can or will turn different color during or after a rain.

My concern, I guess if I were doing it myself (instead of depleting the world's source of aluminum) would be the integrity of the paint skin or film. I would think any contaminants or organics, et cetera could weaken the integrity of the paint or worse. I guess that's a consideration with any paint from the literature I've read, as well as making the pigment particle sizes equal. Correct?

Also, I suppose it can become quite a science if certain aspects are achieved, ie. different properties to obtain a earthtone from say soil, or a vermillion from say a quartz rock?

Lee

[PhilS]

You're absolutely right, K. Lee,
A friend brought me some beautiful pigments she bought in an open marketplace in Turkey (I believe). I haven't used them because, like you, I worry about their chemical stability (if that's the right word). I'm making a living from my paintings and can't afford any nasty surprises...
Would be nice, though, to be able to obtain your own pigments from nature. Aside from Roussillon, I have never seen where pigments actually come from.
Phil

[Anonymous]

I've been busy grinding up more specimens. I just did what I call, "Maroon." It is indistinguishable from Rublev Hematite in hue.

Drawing from my science major education, I think I can take the chance of using these colors. They are washed, filtered, and gravity centrifuged. They didn't come from any especially acidic, or alkyl soil.

I would also like to point out the masters who invented, and perfected ET didn't have scientific knowledge to take comfort from. The ochres they used were dug up from Italy's dirt. There is ochre and charcoal cave art that have stood the test of time.

There are those who will argue grinding mineral particles to an even size is the wrong way to go about things. My tumbler minerals are smoother. They would make great watercolor pigments. I have noticed, to these eyes, their solid stokes are less lively looking than the hand ground.

I guess I am not terribly concerned about using these materials. Believe me, though, I am very understanding about your reticence, given the reputations you've built for yourselves.

Vince

[K. Lee]

That may be the truth, but as a painter, I haven't yet used a egg emulsion. I do experiment myself, sometimes, and there are a number of reasons for me to use or not use a media or medium, some personal, others time, want, space, and some I probably don't know. Basically, besides what I call art however (I feel I'm too blessed with my openess and maybe originallity), I play dark horse. That is I try to congenially make aware exceptions or dangers that I think someone could poke their nose into unexpectedly. That's a plus besides the art of conversation.

With what I do, and have done, and know, I feel artists as a profession don't have it easy, and need to mind themselves in regards not only to their work habits or materials but also their health. Better to be the exception then the rule sometimes especially when someone could easily overlook something.

I should add that I've learned a great deal from the conversations here. Oddly enough, I was contemplating a while back to write here a topic for artists to visit a sight outside of their "exchange" or common medium for comparison, contrast, or to regard the nature of their art conception as I do, more completely . Perhaps in some weird priority I'm blessed here as an oil painter because I've developed a great deal in concept and construct of a painter here, I think. I don't know how much an egg tempera artist would benefit from a site on oil painting, but I don't imagine the relevence of priority is that backwords, if you would, and could open some thought-waves. I find the more I'm open to regarding art the more I improve, and maybe by stepping out of one's own acceptance or nature, someone else can also become better at what they want.


Lee

[Anonymous]

I finished the strong colors. Now I am working on the, "Pastels." These are, in ground mineral form, very cheery, and unusually hued pigments. I call them, "Pink, flesh, and violet." These colors are more transparent than the yellow, red, and brown ochres, which are, in turn, more transparent than their commercial counterparts.

That brings a question to mind. The Iconofile website makes a big deal about the greater transparency of the ancient pigments. They clearly prize translucent pigments. Some of you have studied the medieval paintings that used these colors. How does one know the earlier pigments were more transparent? What are the ups and downs of opaque, vs, translucent?

Vince

[K. Lee]

You have to go to school to know why transparent colors are more valued. ;) Just kidding. That came from the relative weight of this conversation, like many in depth topics. We're going to have, well maybe I shouldn't say. :D

I think, imagine off the top of my head, that because opaque has covering power, an artists mechanical or decisiveness can be obsure to whomever would be evaluative . That would probably be an academic or competitive stalling, or maybe a merit for fineness if not other things. I find transparent watercolors tend to let light into a picture, offer depth, and give a sense of fluidity as well. These things are probably a kin to a good glazing technique in oil or other.

If there is such, I'm sure ancient through classical times applied different meanings in how they brought about art, and as such, I don't have an answer.


Lee

[Dennis H]

Hi Vince,
I love using pigments that I've collected in the wild. If you have the chance to pick up a copy of the book, Colors from the Earth, by Anne Wall Thomas, it's worth a read.
I live in Georgia (US) where there are many fine iron oxides in the ground, ranging from clear yellow to deep purple. I also come across hillsides of pastel colors mixed into white clay (there is a large source of kaolin in Georgia) but most of those colors are not very useful due to low pigment saturation and high clay content. I did make some gesso one time from the white dirt I found, just for kicks. Once I rinsed out the sand and other contaminants, it worked quite well, it was just faintly pink-hued!
I wish I could find some green earth in the field -- I know they occur in this part of the country -- but all I find are spots green from organic matter, which, of course, you can't use. If you dig any up out there, I'll trade you for some Georgia red clay.
Don't get me wrong, I prize my commercially acquired colors, too. Yet there is some curious satisfaction to just pulling the stuff out of the ground. (But then, I also like foraging for morels and chanterelles...)
Dennis

[Anonymous]

Dennis H., pleased to meet you

Your work on display is thought provoking, humorous, and excellently composed.

Yay! someone who knows the joy of collecting. I'm going out to the pine belt to gather more clay, and you can bet I will be keeping an eye out for Morels.

I've heard the Appalachian range is a good ochre source.

I have lots of great reds from orange to maroon. The bright yellow sounds interesting. I have a green tinted sandy earth. I haven't processed it. Grinding as is, it is very transparent. It gives a soft greenish tint. A friend of mine brought it from Nevada. I also have a green earth from California, but not much. I'm wary of it.

My flesh tinted clay is weak as well. It will make a good glaze. The violet kaolin has excellent covering power, and body.

Vince

[Anonymous]

Another note on my Green Earth. I found my old journal I made when I collected, and processed my collection. The local green is a true mineral color. I just ground what I have for some length of time. What I got is a Jadite green. it is muted, and tends toward yellow side of green. It is very transparent. It must be brushed with a soft brush, because it is difficult to brush evenly, and must be laid on. There are two subtypes, dark, and light. I know from my journel where they are in good quantity.

Still, I wonder, why on green earth would one want to use Green Earth for under-painting skin tones?

Vince

[DLH]

Vince,

Here is a demonstration of the traditional use of green earth for underpainting skin tones. http://mywebpages.comcast.net/f.wessel/tech.html#

Doug

[Dennis H]

Vince,
I've done figurative work for a good 25-30 years, in lots of different painting media, and my work is a little less "naturalistic" now than it used to be. I didn't use a green underpainting wash until just a few years ago. However, since I started putting a green earth/verdaccio or, sometimes, a chromium green oxide underpainting similar to the demo seen on Fred Wessel's site, I am entirely more happy with the skin tone results. I had always tried to put blue-ish or green-ish nuances into my faces, but they often seemed applied to the surface, like eye shadow makeup rather than tones from within. The subtle green really sets off the fleshy pinks in a bit of simultaneous color contrast. It's a great effect. Pthalo green and viridian do not give nearly the same nuance, but I've seen artists use them to striking effect.
I prefer green earth over chrome-oxide because it is more transparent and softer in color -- it doesn't obscure my first layer of monochrome modeling. Sometimes, over dark passages the green earth leaves an almost iridescent effect. I know one artist who will only use chrome oxide for the underpainting because he hates the difficult way green earth brushes out.
Dennis

[Anonymous]

Thank you very much, Dennis, and Doug. I will be doing a series of figurative paintings. I kind of guessed the usefulness of the Green Earth to neutralize brighter overpainting. I could see from Wessel's demo, the green was not uniform. When one looks at anything in nature, uniformity is not found often.

The green I get is at the bottom of a very deep road cut in the mountains. It crumbles easily enough. I have to work at getting the right consistency for brushing. Odd that it clings to the glass plate so well. Maybe the for ET gesso will hold Green Earth better than the treated paper I am doing swathes on.

I'm adding on to this post. I just tried my, "Dark Green Earth." Both shades come from the same deposit. the dark green looks very good. This is greener, less yellow. It is also easier to spread. I can see getting results similar to Wessel's.

[Anonymous]

Dennis, if you would be so generous, what do you use for your initial modeling? Are you using the cross hatching method of applying ET? Are you having troubles with underlayer lifting?

Vince

[Dennis H]

Dennis, if you would be so generous, what do you use for your initial modeling? Are you using the cross hatching method of applying ET? Are you having troubles with underlayer lifting?
Vince, I use one of two mediums for my monochromatic underpaintings nowadays. Either I'll use dilute India ink, or Shiva brand casein, also thinned to wash consistency. I had some slight problems a few years ago with my ink modeling getting a little slick in the darkests areas, causing some initial adhesion problems with the first layer of tempera. It was a particular brand of ink I got in Italy, an obscure name that I don't recall. I started using casein instead after seeing works by Zoltan Sepeshy and Peter Hurd that began with casein. No matter how dark I build the casein up, I never have problems with the egg not sticking. I just have to guard against building up an impasto texture on the casein.
I do a little of everything in my underpainting -- washes, hatches, stippling, whatever seems right to build up the image. I know I always stop too soon on the underpainting. I'm always eager to get colors on, but too many times, after I've started laying in color, I wish I had taken the drawing both darker and finished to more detail.
For the ET layers, I start off with general washes, followed by hatching (usually in a similar direction, not at cross-directions), and alternating glazes and hatchwork. I'm not real formulaic after getting the foundation set, though. I just mess with it until it seems better, or until I mess it up.
Dennis

[Anonymous]

Thank you, Dennis. Sounds like we share a similar temperament.

[Alessandra Kelley]

A Green Earth underpainting on skin (I also use Chromium Oxide Green sometimes, but it is toxic) gives a lot more nuance to the color. I once painted a face as an experiment using nothing but green earth, white, and red ochre. A thin layer of green over the red looked quite golden, and any admixture of white over green makes it look deep and bluish and shadowy (for that matter, I discovered a thin layer of white over red ochre makes bright purple). Nearly every color I needed for flesh could be gotten out of those two colors and white, layered over and mixed with each other.

When you're mixing all the colors at the surface of the painting, they can get kind of chalky and unsubtle. It's the layers that make the difference.

[Anonymous]

Hi Alessandra,

I have all those colors collected wild, save for the white. For white, I have titanium oxide. What do you use? Your note of white over red is a little alarming. In looking at Wessel's demo, he uses a cadmium. At reading that, I thought to myself, wouldn't that be garish? Perhaps, using cadmium, he doesn't get purple.

I am experimenting with color mixtures, and overlays. I'm sure I will come to a pleasing technique. One thing, I have learned about figure work is, subtleties bring out life.

I am excited!

[Alessandra Kelley]

I use Titanium Dioxide too. I have some Zinc Oxide, but its lack of covering power drove me crazy.

No, no, really, white over red can be really subtle. I usually use a deep Red Iron Oxide; it helps if it has some cool, purply undertones to begin with. It's not quite as bright as Cadmium Red, but then I don't work with really toxic pigments if I can help it.

How it works is, you let the red dry for a while, a few days at least, until it is dry enough not to be picked up by the next layer. Then you mix up some white, pick it up with a largeish brush, and wipe and wring that brush out until it's nearly dry, until you can lay down that paint almost like charcoal with a stump. Then you do so. (Do not do this with your best brushes!)

I probably should clarify that it produces only a comparatively bright purple -- it's not like Manganese violet or anything -- a surprising blue-violet, really pretty which harmonizes nicely with the iron oxide colors.

As for Titanium White, I like it for its strength and have found that I can thin it down to quite transparent if need be.

I'm not sure if medieval and Renaissance folks really valued transparent colors more than opaque. On the one hand, transparent colors tend to be gorgeous; on the other, opaque pigments have a little more flexibility because they can usually be made transparent, whereas no amount of truly transparent paint will become opaque.

I like to use both kinds, transparent and opaque. For example, as I don't care to use the Cadmium pigments, when I need a bright yellow I generally go for either a transparent Yellow Ochre over a mixed cream color, or if an even brighter yellow is needed, a transparent Quinacridone Gold over an opaque Yellow Ochre or Yellow Oxide.

[Anonymous]

Alessandra, thank you very much. I looked you up on the net. Pleased to meet you. I love your images. My education was in the Life Sciences. I love those glassed in exhibits. By the way, my daughter works at the Chicago Institute.

I got the idea medieval painters liked transparent colors through reading Iconophile pages. Maybe the fact that was all that was available at the time for some colors led to their use.

On yellows, I have a chalk based yellow, that is more transparent than ochre, and more brightly yellow. My notes I made when collecting years ago, say I have large quantities of yellow ochre washed, and strained. I can't find that. Luckily, the clay I dug up from the same location is yellow ochre. I just have to process it. My Sienna is more of a golden ochre.

What do you think of Terre Verde underpainting? I have a good large supply of decomposed crystalized green rock. It has all the characteristics of traditional terre verde.

Vince

[Anonymous]

Two more colors of note:

1) A gritty clay green. I have a sack of fist sized clumps of this unusual sandy clay. When filtered, and washed, it grinds into a lovely creamy gray green. It spreads beautifully. It is the color of eucalyptus leaves.

I think my other greens are decomposed soapstone. They are a stronger green

2) Burnt ochre. This is calcined yellow ochre. My ocher is a true yellow ochre, with good bright color. Calcined, it creates an equally vibrant orange.

Yesterday, I stopped at a road cut. there was very fine white sand bands alternating with terra cotta. Here and there were what looked like maroon rocks. They turned out to be sandstone chips skinned with maroon. There were some with bright yellow caps, too.

An even bigger surprise came when I turned the piece of soft sand stone over. there was a fringe of pure turquoise copper. It can be gently brushed off. Does anyone use copper cools?

Vince

[Alessandra Kelley]

I like Terre Vertes. I use the creamy ones for flesh underpainting, as mentioned above. Some, I have found, are quite gritty, and give an unfortunate texture to overpainting, so I use them for glazes and foliage where their twinkling texture is an asset.

By "copper cools" do you mean the blues and greens formed by copper deposits? Because I do use them. I've taken mineral samples of both Azurite (bright blue) and Malachite (variegated bright green), two chemically related copper compounds used during the middle ages in the West and to this day in China. They need pounding and grinding, and if you overgrind them they lose their color because of diffraction problems (they are still useable, but more pale, pastel versions of themselves). They are very gritty (in the middle ages Azurite was called "Blue Sand").

[Anonymous]

The thin copper oxide I found on the trailing edge of the colored soil clumps, is pure, and extremely fine. I am going back, with a fine brush and get as much as I can. I know it is hazardous.

The two Terre Verde samples I processed before have more green. Even with a lot of grinding they remain gritty. I agree, I'd rather use those with glazes. I wish I could remember where the sandy clay lumps came from. The green is consistent, and bound with the clay. It wants to go down opaque.

Do you use any synthetic blues? I have some Lazurite. I need to buy a stronger green, and a couple blues.

I will start painting on my return from NY next month. I am excited.

[Anonymous]

update:

I found I had a wash basin holding plastic wrapped loaves of clay. They had all come from the colored clay deposit most of my minerals came from. Progress has laid that treasure trove under gravel. The bulldozer wouldn't understand the travesty. One clay is pure white. Another is grey. The third is bright yellow. That last one is my ochre. I am so happy I collected it in large quantity 15 years ago.

The grey is a decomposed sedimentary rock. It is pure, without a trace of warmth. It will be great for shadow glazes. It looks blue among among the other vibrant colors.

My wild colors are:

Cold Dark Gray

Warm Near Black

Charcoal Black

Two types of Green Earth, three shades

Three magnificent true Umbers, each of a slight different flavor

Sienna - a rich dark gold

Yellow Ochre - rich and bright - more yellow than commercial grades

Chalk Yellow - true yellow

Fiery Orange - for an earth color, startling

Unique Brown - this is a complex chestnut tinged with violet

Flesh - In powder form Caucasian skin tone. Tempera darkens and warms the color into a brownish peach.

Violet Gray - rich, and opaque

Red - a brilliant Hematite hue

Maroon - an intense dark cold red

Purple Rock - my first collected for pottery purposes. It is a sumptuous velvety deep burnt purple

White - clay. Perhaps handy for those misty scenes.

Copper Aqua - the real deal


Vince

[maperry]

Hello,

I am new to this forum and new to tempera painting. My usual medium is acrylic, but I recently moved to Malawi Africa where commercial paints are hard to come by and very expensive. I have brought supplies with me, but working with local artists has inspired me to address the huge obstacle...lack of access to supplies. I started experimenting with ET last week using the ochre clays, charcoal and papaya leaves I collected from around town. I have gotten great satisfaction tapping into my resourceful side and knowing that my paintings from Malawi are not just about Africa but made FROM Africa. I am hoping to hone my skills both on the production side of ET and painting techniques with the medium, in order to teach Malawian artists how they can use their local resources for painting.

The other obstacle is ground and supports. I haven't found any good paper yet. Honestly the best is card stock. Someone mentioned cardboard in one of the other topics. Is cardboard really a good support? If so, do you need a layer of gesso? We can find canvas and wood. My only hesitation with using wood as a support is that it might limit the artists' market which consists mostly of western tourists who want to buy something easy to travel with. I'm still searching for some kind of drying oil (linseed, etc.) which would allow us to make oil paints and work on unmounted canvas. My only concern here is the price factor...I have no idea what to expect. I'm hoping to do art for the sake of art and process, but reality is that this is one of the poorest countries in Africa. These people need to use their skills as a financial means to support themselves and their families.

I'd love to continue the discussion on preparation of found pigments. I hand ground charcoal which gave me a great black. It resulted in a grainy texture, but was able to work with it and liked the effect. Right now I'm looking for cheese cloth to use as a filter and hopefully be able to make a finer pigment and even paint. Any ideas on making greens? I used papaya leaves which gave me a wonderful brilliant green. But, as you might expect, after only a few days my lime green is turning more and more yellow. Interestingly, the paint I made from boiled papaya leaves is holding the color, but the pigment is more grainy. It appears to not have dissolved into the water. Lastly, I'm curious to know more about grinding rocks to make pigments. I don't have access to a tumbler...although I may be able to find someone who could engineer it for me. But my overall goal, is to use only my hands and natural resources so the process can be affordable and accessible for the artists here in Malawi. Have any of you found ways of making blues? Also, ahve you experimented with organic material like flower petals?

Thanks,
Marissa

[Alessandra Kelley]

Holy cow. What a project.

I can't recommend cardboard as a support. I think the earlier references to cardboard may mean a different sort of thing from the modern product, something more suitable for art. I guess it depends on the quality of what you have over there. If your wooden supports were not very large, if you were painting exquisite smaller pieces, do you think that would work?

Organic pigments tend to not last very long. The rocks are a better bet.

Blues and greens always were tricky pigments. You can go a long way with suggestion -- that is, a black mixed with white tends to make a cool grey, and if the rest of the painting is full of yellows, it can look blue.

I've used a mortar and pestle to grind pigments.

[Dennis H]

I don't know if you have access to a good bookseller or mail order books. A great book you should read, especially in your current circumstances, is "Color: A Natural History of the Palette" by Victoria Finlay.
It might inspire you further in your use of naturally ocurring pigments and help guide you on how to make use of them. Also, it's a pretty fascinating read.
Dennis

[Georgeoh]

Has anybody else any experience, positive or negative, with found colors?
I probably have more experience with "found" pigments than most artists. My company, Natural Pigments, has been extracting many different pigments from the far corners of the earth. Most of our pigments we obtain through our associate mineralogists and I have personally participated in "gathering" minerals and earths.

I find that the range of particle sizes typically encountered in natural mineral pigments offer many advantages in paint to the artist. From a paint manufacturing viewpoint, on the other hand, they are very troublesome because they tend to flocculate in the paint binder during storage, which is why most paint manufacturers, including artists' materials companies, avoid using them in their paint formulations.

The advantages of using paint with larger granular and heterogenous particle sizes include 1) increased transparency (for optical mixing between layers), 2) thixotropic paint behavior (an important property in oil painting), and 3) what I call an "illustory" painting technique. The latter technique invloves painting a layer of color of fine particles over a layer of larger granular pigment crystals. The smaller, finely granular particles of pigment slide off the facets of the larger crystals, making the underlayer of large particles appear to float in a sea of fine particles. It is a different form of optical mixing between paint layers, and one that was often used by ancient tempera painters. I have microphotographs of this effect on 15th century icon paintings, if anyone is interested in seeing it.

[raphaelarts]

George,

I was just reading an article about the same subject. Natural and mineral pigments with thicker caliper, compared to the modern replacement, yield brilliant colors. He also mentions the layering of a thicker coarser layer of azurite "over" a thinner paint layer made of thinner size pigment particles. This is the opposite of what you mentioned.
Which one was the proper sequence, thick over thin or thin over thick?
Raphael

[Salamander]

When you are collecting and after slaking, what size mesh do you screen to?

[Georgeoh]

...He also mentions the layering of a thicker coarser layer of azurite "over" a thinner paint layer made of thinner size pigment particles. This is the opposite of what you mentioned. Which one was the proper sequence, thick over thin or thin over thick?

There is no "proper sequence," it depends on the effect that you are seeking to achieve. A layer of coarse particles over fine particles, allows more light to pass through the top layer onto the bottom layer and back through it again. On the other hand, a layer of fine particles laid over a thin layer of coarse particles, allows the fine particles to "slip" off the sides of the coarse particles and create an effect of coarse pigment particles in a sea of fine pigment particles.

[Georgeoh]

When you are collecting and after slaking, what size mesh do you screen to?
At Natural Pigments, we grind and levigate (it is not slaking) pigments to different particle sizes, depending on the desired color and pigment properties. So the answer is highly variable. For example, we grind and levigate (and at times use electromagnetic fields) to separate azurite particles into the following ranges: 0-45 microns (less than 325 mesh), 45-74 microns (less than 200 mesh), and 100-150 microns (less than 100 mesh). However, most ochre, siena, umber pigments benefit by further grinding and levigating to obtain the finest particle size possible. However, even these will be larger and less homogenous than modern artificial pigments.