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Old 23-07-03, 03:28 PM
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RobM RobM is offline
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Default Ultramarine Blue

Some years ago I noticed a white residue in areas that only contained ultramarine blue. It was brushed away with a soft clean paint brush. It did return a few more times but now seems to have stabalised. The painting was done in 1996.
I also notice a white crystal type substance on the inside of my ultramarine paste jar. The substance is so light that I can just blow lightly into the jar and it disappears.
In a paper presented to The Society of Painters in Tempera by P. Tudor Hart on July 8th 1922 states...
"This pigment requires most careful manufacture to ensure its stability, its richness and pureness of colour, and as far as possible the elimination of the soluble sodium salts and the excess of sulphur. This latter is rarely, if ever, eliminated."

He goes on with a warning...
"One of the great disadvantages of ultramarine is its characteristic property of being readily acted upon by acids, even by the weak organic acids. I therefore warn Tempera painters against the use of a few drops of vinegar in their egg when tempering ultramarine."

My question....is the white residue salt?

Rob
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Old 24-07-03, 01:54 AM
hisstah hisstah is offline
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Hi Rob,

Did you prepare the paste yourself from dry pigment or is this a proprietary mixture? Are you seeing this happen with *all* your paintings where you used this pigment or is it this one painting?

It could be caused by a number of things, which is why I asked. I recently read an article published by the Getty Institute. The author was examining a number of paintings in tempera by an African-American artist--can't remember the artist's name at the moment. But he worked in a combination of materials, one of them proprietary mixtures of egg tempera.

Apparently, some of his paintings done using these tubed egg tempera paints are exhibiting similar problems to yours. (Many of these paintings were done in the '50's.) The solution is the same--gentle brushing away of the white powder. The author theorized that the powder was an impurity included during the manufacturing process of the tubed paints. I don't have the article here at the moment and can't remember if they did an elemental analysis of the powder. If you're interested, I'll get the article from work tomorrow.

I've seen something similar in oil paints, too. To keep the cost down, some manufacturers add stearates--I think that's the correct spelling-- to the paint to bulk it up. These stearates can effluoresce onto the surface over a period of time, creating a powdery, hazy appearance.

That's why I wondered if your paste was a proprietary mixture. If so, it's likely an impurity and you might consider discarding it. I'm glad it's not made a reappearance on your painting since the last removal.

Sincerely,
Lorraine
  #3  
Old 24-07-03, 02:56 PM
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Lorraine,
No it's just Cornellisen's finest pigment.
I've just had a good look at this residue under a magnifying glass. It is definitely a crystallisation, almost like snow but very irregular and only about 1mm in size.
I would scan it but it is so light that it just floats away in the air.
I've had no problems with painting with the pigment, except that one painting which as I mention has stabalized.
I do not get his residue with any other pigment.
Can't afford to throw it away......it's a 2KG bag!!!
Rob
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Old 25-07-03, 03:21 PM
Alessandra Kelley Alessandra Kelley is offline
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I too have gotten a fine white crust on the rim of my jar of ultramarine blue (from Kremer), rather like the dried pigment powder I sometimes get on my other jars. It has not formed on my jars of ultramarine red or ultramarine violet. It doesn't seem to have caused any harm, or manifested in my paintings, but it is weird.

Actually, I just popped down to my studio to check and, jeepers creepers! I've got a curtain of fine crystals hanging down under the jar lip more than a centimeter long! They look rather cobwebby, or like dandelion seed heads.

Could the sodium in the sodium aluminum sulfo-silicate be reacting with something else?

Alessandra
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Old 25-07-03, 05:56 PM
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Alessandra,
You certainly add to the description of what I find.
I've had a PM from Lorraine who has made some suggestions.
It seems to be a definite impurity within the pigment and so far has had no detriment to the majority of my work.
The 'crystals' seem to congregate around the rim and the lid and not on the pigment paste itself. By just removing the lid and giving a gentle blow they all disappear.
I have no concern about it but just was inquisitive to know what it was.
Maybe it is efflourescence as described by P.Tudor Hart. Non of the manufacturers seem to have come up with any modern ideas to remove it.
I'll live with it!
Rob
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Old 29-07-03, 08:09 PM
Rosemary Rosemary is offline
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Default salts

I would guess that the stuff is sodium chloride or sodium sulfate. But the description of it being very light might indicate sodium bicarbonate or sodium carbonate which would occur if the pigment had a residual amount of excess sodium ions present to maintain its basic nature to be more stable.

Sodium chloride has colorless cubic crystal shapes, sodium sulfate heptahydrate has white rhomboid or tetragonal crystals, sodium alluminum silicate has colorless hexagonal crystals, sodium aluminum sulfate has colorless cubic octagonal crystals. sodium carbonate heptahydrate has white rhomboid bipyramidal efflorescence.

So if you can look at the crystals with a magnifier, you might get an idea which of the above is contaminating the pigment, unless it is a mixture which will affect the crystal shapes.

As the stuff is water soluble, successive suspension of the pigment in water, letting it settle and decanting the water several times should remove the bulk of the salt. But I have had the problem of wet ultramarine blue solidifying in the jar.

I have not had salt efflorescence with ultramarine blue, but I store it dry and mix with water just before using. I am using ultramarine blue dark from Old Holland.
 

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