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View Full Version : Museum visit, how'd they get those whites?


capnd
03-29-2019, 08:41 PM
I visited chicago art museum today and was treated to a few rembrandts, a titian, several rubens, el greco, dozens more from the baroque era. Lots of fun.

I wondered how the old masters made their whites so opaque, given they used lead white. I have used WB and MH cremnitz and have found them both to be semitransparent at best. Never used OH cremnitz, which is reported to more opaque, but I cannot see it being that much more opaque.

So was it just a more opaque mix (mulled stack process), fillers (chalk), medium (egg bodied oil)? My way is to just build the opacity in layers, but can't always do that in which case i mix in some titanium.

Seems we are a bit spoiled by Titanium and its instant opacity.

plnelson
03-29-2019, 09:05 PM
... not only that, but any white from that era by now has been heavily worked-on by conservators, and conservator work often involves retouching, not just cleaning.

capnd
03-29-2019, 09:54 PM
you know it. i colourex'd the pigment analysis on a few of them already. madder lake glazes that looked like they were painted yesterday. certainly not after 500 years. ah well, it brought out the artists intent .. simply stunning to see.

WFMartin
03-30-2019, 12:06 AM
I believe that the old masters who used Lead Whites made them appear "White" by surrounding them with a load of "darks"--especially Rembrandt. It is more a visual thing, or optical illusion than their having used some sort of a unique type of White paint.

Gigalot
03-30-2019, 04:54 AM
They also used Eggshell white. Said to be best calcium carbonate white ever.

AnnieA
03-30-2019, 11:19 AM
They also used Eggshell white. Said to be best calcium carbonate white ever.
For those who like to experiment there's a 16th century recipe for it under the eggshell white entry on the Color of Art Database: http://www.artiscreation.com/white.html#eggshell

Gigalot
03-30-2019, 12:06 PM
For those who like to experiment there's a 16th century recipe for it under the eggshell white entry on the Color of Art Database: http://www.artiscreation.com/white.html#eggshell
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!

Pinguino
04-01-2019, 11:55 AM
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! Alex, do you know of any pre-made (tubed) eggshell white paint brand?

Seems to me that although there are a lot of chickens in the world, and a lot of eggs, pigment from ground eggshells might be expensive. Not a lot of material in an eggshell, and it must be purified.

NOTE: For the benefit of those who found this thread via Internet search: We are talking about artist oil paint make with ground-up eggshells as white pigment. We are not talking about the color "eggshell white" of house paint, which is not made using real eggshells.

Gigalot
04-01-2019, 03:46 PM
Alex, do you know of any pre-made (tubed) eggshell white paint brand?

Seems to me that although there are a lot of chickens in the world, and a lot of eggs, pigment from ground eggshells might be expensive. Not a lot of material in an eggshell, and it must be purified.

NOTE: For the benefit of those who found this thread via Internet search: We are talking about artist oil paint make with ground-up eggshells as white pigment. We are not talking about the color "eggshell white" of house paint, which is not made using real eggshells.
I can agree. I did my own Eggshell white. Before grinding, you must remove thin film (protein?) from from crashed eggshell.

plnelson
04-01-2019, 03:59 PM
Eggshells are mainly CaCO3, as is chalk and the shells of a lot of marine organisms and a lot of other naturally occurring stuff. Now granted calcium carbonate has a variety of different polymorphs, but does anyone know why eggshell calcium carbonate should be whiter than other forms?

Gigalot
04-01-2019, 05:07 PM
Eggshells are mainly CaCO3, as is chalk and the shells of a lot of marine organisms and a lot of other naturally occurring stuff. Now granted calcium carbonate has a variety of different polymorphs, but does anyone know why eggshell calcium carbonate should be whiter than other forms?
It has opaque structure.

Pinguino
04-01-2019, 08:14 PM
It has opaque structure. 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.

Pescarolo
04-02-2019, 07:49 PM
OP Welcome to Chicago! The art institute is a great museum.

Stack Lead White by Michael Harding seems to be the best (or among them) for replicating the qualities you describe. It is an ancient process that involves suspending lead over vinegar, covered by horse dung. The vinegar vapors turn the surface of lead to lead acetate and the poo vapors turn it to lead carbonate.