I have recently found a good source of more or less affordable azurite. The pigment is beautiful, easy to work with in egg tempera. Its shade is also easily controllable by grinding more (it gets paler as you grind it). However, one issue that I found bothers me a bit. When I finish the work, it is a beautiful tone of blue with a hint of green in it. However, after a few months, it gradually turns more and more green. Not entirely objectionable, and in fact the color harmonizes better overtime. But is there a way to stop it from greening? I read somewhere that many egg tempera works and frescoes were done in azurite but it didn’t green.
Thank you, Brian! That’s probably the cause. I grind azurite either with water and keep it in a small jar and temper right before painting; or in some cases, mull it with egg emulsion for proplasmos (base coat) application. Looks terrific for a few months, then greens. So this must be the case. I work dry-brush, so there is no “wet” or petit lac application for the the smaller particles to “green” the coarse ones underneath.
I grind my azurites as little as possible both in tempera and in oil. Because it is a relatively ‘soft’ mineral even a couple of turns with the muller affects its blue colour.
Dear Brian, Having read your comment on azurite turning green after prolonged period in water, I checked a small jar of azurite I ground with water about 2 months ago. It is as blue as when I ground it, no color changes. I painted a small detail with it, and it hasn’t changed color. I shall see how it develops in time.
In general, azurite does not become more green in egg tempera on its own. The pigment is known to become greener when kept for prolonged periods in moisture or water. It is for this reason that it is suggested that the pigment be ground in water just prior to use in either tempera or fresco. What I have experienced when working with azurite in egg tempera is that the finer pigment particles rise to the surface of the paint in the well and even on the panel if it is applied in a relatively wet manner. In essence, the duller and greener particles are covering the bluer, and more brilliant, azurite below. Azurite, being a copper carbonate, is reactive and can discolor in the presence of free sulfur although I have never experienced any issues with this in tempera. Azurite can, although not always, darken and become greener in oil. This is especially exaggerated when the artists adds too much oil to compensate for the difficulty applying and brushing a paint containing the coarse pigment particles necessary for creating a deep blue with azurite. Finally, and this is a separate issue, if a work containing azurite is varnished with a coating that will yellow over time, the yellowing may be more evident in this pigment due to the coarseness which traps and holds a lot of varnish contributing a more greenish tone to these areas. Please let me know if none of this seems to describe your problem and I can ask seek out the expertise of some of our other moderators and contacts.
I have also kept azurite in water for longer periods of time and not noticed any change in the jar. I have wondered if it requires time in the presence of oxygen to complete the transformation. It would be instructive to keep some in the jar and paint some out and compare them after longer term aging. Let us know the results of your experiments.
Ahh. Yes, I mentioned this possibility in my initial answer. So glad that you figured out the problem. You may eventually want to rethink your use of Olifa. The boiled oil and oil containing varnishes called olifa will always yellow strongly and are irreversible. You can read more about oil varnishes in our pdf download in our resources section. The historical use of olifa is greatly exaggerated. The technical director if Iconofile and Natural Pigments, George O’hanlon, has commented on this many times. We would be happy to start a thread about the advisability and use of olifa if that is of interest to you..
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