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A traditional, inexpensive way to extend and thicken paint is to use marble dust, a.k.a. calcium carbonate. This should aid drying. I haven’t really noticed a leveling effect on the brushstrokes — but then again, I tend to paint thin
Lately, I’ve just been mixing up some loose calcium carbonate powder with some of Art Treehouse’s water-washed linseed oil right on my palette to make the putty material that Tad Spurgeon writes extensively about on his blog (https://www.tadspurgeon.com/content.php?page=putty+tutorial). I’m pretty happy with this, as it’s easy to control the consistency, and it seems to make sense to mix only the amounts one needs for that session.
Regarding the putty, note that I’m not certain what sort of difference it might make to use artist’s refined linseed oil in place of the water-washed oil he recommends. Also, I understand that one should use a mask when working with calcium carbonate powder as it can be a respiratory irritant.
That is all there is to it – mix the powder into some oil until you get the texture you want. Test it by mixing into your paint and adjust the amounts as needed.
Limestone powder is a type of calcium carbonate as are chalk and marble dust. The grit size of the powders used will influence how they react in the oil. I prefer the way fumed silica behaves in an oil gel vs the calcium carbonate paste like materials. You can make your own silica gel as well by adding fumed silica to linseed or walnut oil, or you could try both to see what happens. As already noted, wear a mask when working with powdered materials. Fumed Silica will float in the air with the slightest bit of air movement so take precautions.
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CalciumCarbonate in linseed oil mixed 1:1 with regular oil paint is fine for glazing.
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Catie George wrote:Pure calcite, as a large crystal with few impurities, is very transparent. "Spar" calcite (very pure, very clear large crystals) is quite interesting, as it's known for double refractions - you see two images side by side if you look through it. I wonder if that would impact the apparent "glow"?
Catie George wrote:
Basically - looking at the optical properties of pure calcite, i am not surpised that fine, pureground calcite would behave with a lot of transparency when added to oil. (And i wonder about silica dust, though likely less safe to work with).
Edit - After musing some more with respect to the transparency of calcium carbonate, i'd anticipate the SOURCE of calcium carbonate to make a big difference for transparency, possibly more than it's exact particle size/distribution, even with the same chemical formula, with a rough opacity scale of chalk (the kind from microscopic creatures) -> llimestone dust-> marble dust (ordered with increasing transparency). Marble is limestone after heat and pressure mushes it together and allows the crystals to rearrange themselves to be bigger and less flawed.
Getting way into the weeds - i wonder if particle size distribution also matters? For example, if the calcite crystals and the pigment crystals are both of consistent particle size, but have a gap between them (so the calcite is consistently smaller or bigger than the pigment) , i'd expect them to behave differently (smearing seperate, or settling from each other) in paint than if they were consistent. I'd also expect if you have a wider range of particle sizes of calcite, smoothly graded between them, your paint will likely be better at holding it's shape.
Eggshell White [KP.p];
Calx de tistis ovorum;
Shell White
Powdered egg shells; mostly calcium carbonate; Brown eggs contain Ooporphyrin with a small amount of biliverdin with 2-3% eggshell pigment; (Ref)
Recipe from Secrets of Alessio Piemontese, 1557:
"Take fresh well washed eggshells, which are the pureset white, and grind them with the cleanest water on a marble slab until they are perfectly ground. Then put these crushed eggshells and water into a clean bowl, and let the powder settle to the bottom and then drain away the water carefully and allow the powder to dry naturally and you will have an incomparable white which cannot be surpassed by lead white or any other white in the world, if it is made carefully and well.." - (*Secreti di Don Alessio Piemontese [Secrets of Alessio Piemontese], 1557).
White; light brown*; light blue*
† Any tint is from natural protoporphyrin, ooporphyrin and biliverdin (brown) or bilirubin (blue) and will quickly fade, however the white from Calcium Carbonate will not.
Used as a white in watercolor and fresco in olden days, also used as a base for lake pigments and filler / extender in oils.
* Any coloring other than white is fugitive;
Not rated by the ASTM, calcium carbonate has a long history used as a pigment and will not fade from sunlight. However it can become discolored with age from atmospheric pollution, dust, smoke and yellowing of the binder. It is also susceptible to chemical breakdown from acids
They are wrong about transparency in oil of Eggshell white paint. I can agree, that Chalk and Marble dust Calcium Carbonate is totally transparent in oil, but not eggshell white. It is opaque, the opacity can be comparable with Zinc White or Lead white. Such pigment contains sealed air bubbles, that gives surprisingly good level of opacity to it. After grinding with linseed oil it has fantastic rheology to use for layered portrait technique!
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r ransom wrote:
Calcite as I keep calling it may not be the best word, but easier to spell than calcium carbonate, seems to have several paths to aquire it. Limestone, marble, chalk...and possibly eggs.
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Syd Smith wrote:
r ransom wrote:
Calcite as I keep calling it may not be the best word, but easier to spell than calcium carbonate, seems to have several paths to aquire it. Limestone, marble, chalk...and possibly eggs.
I think calcite is fine! Limestone, chalk (a type of limestone), and marble are usually all made of calcite, or sometimes dolomite (a magnesium calcium carbonate), but calcite is the most common mineral in all of your sources. Aragonite doesn't survive geologic conditions as well and tends to be replaced by calcite, so it's typically much more minor. The real differences between your sources should be the grain sizes and habits (shapes) of the calcite, rather than the mineralogic makeup.
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Indeed. Generally, a paint gets opacity for one or both of two reasons: 1. The individual pigment particles are opaque; 2. The index of refraction of the pigment particles is very different from that of the surrounding medium.
Many mineral substances are nearly transparent in bulk crystalline form. When ground into powder, the tiny particles are nearly transparent. But nevertheless, when bound into a painting medium, the paint is opaque or nearly so. What happens is that each time light encounters a medium/pigment boundary, a portion of it is deflected. So many thousands of little deflections happen, that the tiny amount of per-particle absorption is compounded. This kind of pigment is often white or light-colored, since a lot of the deflected light bounces back out.
Quantitatively, the above effect is a function of the difference between the index of refraction of the medium, and that of the pigment particles. Titanium Dioxide has a very high index of refraction compared to any painting medium. Thus, TiO2 paint is very opaque (and very white). Lead Oxide has a lower index of refraction; Zinc Oxide even lower. Thus, these pigments produce less-opaque paints.
When oil paint cures, its index of refraction increases slightly. So, the difference in index between pigment and medium is less than before. As a result, the cured paint is slightly less opaque than when it was wet. The difference is not noticeable for Ti02 because the indices are so different. But for some other pigments, including a few of the natural and synthetic earth colors, there is a noticeable difference.
Some pigments can chemically react with the medium over time, but that’s a different issue.
In the case of eggshell, at the microscopic level the powder is not solid crystalline CaC03 (which has an index of refraction not very far from oil). It is a matrix of air (which has an index very far from oil) trapped within CaC03. I believe, but am not certain, that such paint will actually become slightly more opaque with time.
You can see the effect every day. Water is clear. Air is clear. Water with many tiny air bubbles is not clear. This is due to light reflection and diversion at the many air-water boundaries, because the materials have very different indices of refraction.
Note that for some pigments, such as Venetian Red, the tiny particles are themselves opaque, quite apart from the effects of refraction.
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Marble dust is used for a number of things as I work my way through the painting, it can be mixed with oil to create an extender for oil paint that doesn’t affect value or color much while increasing the transparency a bit. It can be used to thicken up paint that I have diluted with oil, and can be used to help clean up my palette when I am done. When used as an extender, the paint tends to grip the surface, staying where it is put, so I use this heavily in the middle layers of my painting.
Because all this is done alla prima, very little concern is given into how much oil I am using in the painting, it’s all going to dry at about the same rate (nothing is going to dry dramatically faster than the rest). After finishing an alla prima session I will often allow the paint to cure at least a week then come back in and glaze some colors as needed.
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I was a bit confused by some of your comments. Perhaps this will clarify things a bit.
Calcium Oxide – Chemical Formula CaO – As you noted, this is not something you would want to add to your oil paints, grounds or mediums other than for Fresco.
[INDENT]Calcium oxide, commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term lime connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate.[/INDENT]
Calcium Carbonate
Used in various forms – Chalk, Marble Dust, Diatomaceous Earth – Chemical Formula CaCO₃ – is a very common additive for oil paints as well as painting grounds. (Quotes are mostly from Wikipedia)
[INDENT]Calcium carbonate is a chemical compound with the formula CaCO₃. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms, snails, and eggs.[/INDENT]
Chalk
[INDENT]Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is an ionic salt called calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells shed from micro-organisms called coccolithophores.[/INDENT]
Calcite
[INDENT]Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate – CaCO₃. [/INDENT]
Marble
[INDENT]Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite – CaCO₃ . Marble may be foliated. In geology the term “marble” refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone. Marble is commonly used for sculpture and as a building material.
[/INDENT]
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Chalk is very near colorless in oil, it actually adds transparency and body to a paint. I use a form of it called marble dust, and it work wonderfully for adding body and transparency to the paint when mixed with a bit of oil. Strongly suggest just trying it if you have some on hand, mixing some oil and chalk or silica together with a palette knife. Add drops of oil to your powder and blending with knife until it is the consistency and color of an off white paste, add a small amount to your paint to see how it works and apply that on a piece of extra heavyweight paper or other cheap substrate to allow it to dry.
Try sedimented Calcium Carbonate. It is made from lime solution into water by pushing Carbon dioxide gas through. Such Calcium Carbonate has finest particle size and it is completely free of yellow iron oxide impurities. Sedimented Calcium Carbonate is paint grade stuff and used to manufacture paints, not gesso or putty.
Dick Blick sells Marble Dust[/URL] by Fredrix. From the information I gleaned years ago, the particle size is extremely fine ( < 300 mesh or 30 microns ), my "putty" made with it is a very slightly gray white color, and very transparent when mixed in with paint. Various pottery suppliers sell a very fine version of marble dusts and chalks as well, some 270 mesh (which is <30 microns in particle size). The Fredrix variant is extremely consistent in particle size.
They are absolutely different things. How can you compare 30 microns powder with 0,3 micron materials? If all those fillers are chemically CaCO3, that do not means they are the same in light reflection, rheology, gloss, oil binder saturation e.t.c with thousand different physical and optical properties. How many times I heart, that Calcium Carbonate are poor, gritty, sandy, grayish cheap material from hardware store. Did you try sedimented Calcium Carbonate instead?
Also, they are thinking Calcium Carbonate is completely transparent. Try Egg Shell powder instead of hardware store stucco. You will see it is almost semiopaque white.
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I can vary drying time of pure Titanium White in safflower oil binder form two hours to two days by using differen amounts of Alkyd/Calcium Carbonate oil paste into it.
Calcium carbonate paste I use for slower drying. All my problems with paint drying time are in the past
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Delofasht
Chalk or marble dust mixed with linseed oil makes that putty that Tad likes. I do actually use this putty in my finished paintings but one is unlikely to be able to notice it visually. It tends to make paint more transparent and can make some colors more oily and behave slightly differently in impastos, but it is wonderful for large flat areas. Layers involving this kind of extender dry more matte and allow for added layers to adhere very well. I am personally a big fan of the stuff, it has allowed me to use just a tiny bit of paint for much larger areas of color than I would have expected and in generous thick applications as well. I find it works better with artist grade paints than student paints though (which already have a good amount of extenders and fillers in them).
I think you will learn more about paint and painting by making your own calcite medium. Although clearly opinions vary, some of the greatest painters in history have heavily used calcite based mediums and there is no grounds to dismiss such inclusion as less that what is required for producing masterpiece work. Aside from other considerations, calcite inclusion is likely to, in general, increase the archival quality of your work. You can get chalk from pottery supply places for a couple of bucks
All those fillers gives different result. Calcium reduce brush strokes and improves fluidity. Talc gives matte effect and prevents pigment sedimentation.
Wollastonite and Feldspar improves durability and flexibility. “As an additive in paint, it improves the durability of the paint film, acts as a pH buffer, improves its resistance to weathering, reduces gloss, reduces pigment consumption”
Silica prevents abrasive deterioration
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Actually I’m just experimenting with this now. Seems to work very well for increasing transparency. Densely pigmented tube colours tend to obliterate everything beneath but cut with putty medium they seems to have a lot more depth and “air”. My understanding is that these putties are naturally lean as not much oil is required to make a workable paint. They are reported to dry well (depending of course on the oil component) and to increase adhesion. Also claimed it makes for a good paint film (especially with a bodied oil component) and more or less non-yellowing. As the chalk basically functions as a filler, the non-yellowing thing if it is true seems a bit hard to explain. The leanness of the putty may be at work here (little oil, little yellowing). So basically it just looks like a big win all around :-) In the few occasions I have seen Rembrants in the flesh, I’ve marvelled at the wonderful transparency, particularly in the darks. This makes a great contrast with his strident white highlights. Very difficult to do with modern tube paint sans using ridiculous volumes of solvents/oils, and impossible whilst retaining body. I’ve read a number of sources that say he used chalk. Simple and effective it seems! Go forth and conquer!
Yes, lots of different effects can happen based on what you want the paint to do. It is a stable way of making modern paint a little more like older paint. As you say, the refinement over time is really fun. A nice place is one where the paint can be changed or moved around with bristle brushes, but then blended or cleaned up with softer brushes.
Well, with my work, I got involved with hand-refined linseed oil, so it all dries overnight. This is not hard to do, happens naturally with the hand-refined oil, but I’m exploring longer open times for layers now too with poppy or walnut oil. Sometimes overnight is too fast! But yes, I have lots of things in progress. I wish they would hurry up. To some extent this is the result of writing a book about the materials, needing to cover all the zigs and zags. But I like that feeling a painting gets when it has emerged from a struggle, too. At first it feels impossible, but then gets solved somehow. It’s always kind of a duh moment too, like I should have known it all along. But still the best part for me.
Thanks for adding to the discussion Tad.
I have used calcite in one form or another in my paintings for the last few years. Pretty much since I started to paint solvent free.
There is a tremendous amount of great information posted by Tad and I can say that his results are confirmed by my own experimental results. It is actually a pity that there is so much miss information out there regarding artists materials. For example Gottensen “the painters handbook” says that washed linseed oil doesn’t dry faster that raw linseed oil. This simply is not true. Water washed cold pressed linseed oil dries (cures) at twice the rate of unrefined oil.
Regarding calcite; it is great that the use of calcite is becoming more respected and know amongst artists. I notice that Gamblin are not at all ashamed of the inclusion of calcite in their student range . And, judging by the handling of the paint, their fastmatte paint also contains calcite. And all power to them, they are nice paints. But the artist can make their own underpainting equivalent by combining a fast drying burnt umber ground in linseed oil e.g Old Holland , and combining that with a combined calcite/ Alkyd-walnut medium (thanks M Graham).
I think that the modern artists owe it to themselves to do at least a little experimentation with calcite. For my part I mostly use a thin couch medium containing calcite. Much like a pigment free paint but oh so much cheaper and in my control. I can blend translucent thin layers into this, where intensity is determined by the amount of pigment not by a blend of pigments. The calcite allows better control of that magic window of not too much oil and not too little.
I think that modern artists should be moving to regain the intellectual property of paint characteristics and behaviour from the paint manufacturers. It has been well lamented that there are not modern schools where painting technique can be learnt. Heck, I spent 3 years at university in fine art but no one taught me how to control paints rheological properties!
Kudos to Tad for providing solid information! Personally I have travelled a similar path and realised that my (expensive) shelf full of resins and mediums is largely unnecessary. Vergil Elliot makes similar comments that have taken me too long to accept. There is magic in dirt ground with linseed oil…..
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