Monday, April 19, 2010

Making Azurite

Azurite is a blue copper mineral, directly related to malachite. They are nearly identical chemically, only very small but important differences make for the color difference. The two minerals are similar enough that they can often be found surrounding each other in the same rock. In fact, given enough time, azurite would eventually become malachite if left alone in nature.

Nowadays its easy to take for granted the large selection of blue pigments at our disposal. Several hundred years ago choices would have been more limited. Azurite was the cheapest and most available mineral source. It was for the same reasons I chose to make my first blue from azurite.

The color of azurite varies considerably, depending on how it is ground. When it is coarsely ground, like a fine sand, it is a very deep, royal blue. The finer it is ground, the paler it becomes. Painters could choose to take advantage of this quality. To make my pigment, I used the same levigation technique as I did with malachite. This would provide me with several different particle sizes.















The azurite as purchased. This was a nice sample. It was easily ground into a coarse powder.















I added the dilute egg yolk solution.















I decanted the mix a few times into separate bowls. The bottom bowl is leftover. The discolored gray appearance is due to impurities.















I poured off the rest of the liquid, removing most of the impurities. You can really see here how the color of azurite varies depending on how fine the grind is.

I repeated the refinement process several more times, regrinding the powder slightly finer each time.


Update: I was having some problems with the egg-yolk solution. Separating the finest particles from the leftover protein was difficult. I've switched from using egg yolk to a casein solution. I made a textbook tempera casein solution and let it sit overnight. The next day I highly diluted the mixture and then used it to levigate freshly ground azurite.















This change has allowed me to separate the smallest particles much more easily, with less waste. I was surprised by the beautiful new purity of color I was able to achieve.

6 comments:

Jules said...

I've recently seen azurite levigated with water and it produced some lovely blues. Does adding the casein solution do anything other than speed up the process? Is it easy to wash the casein out of the pigment before drying it?

Zachary Kator said...

Jules,

Thanks for the questions.

There's nothing wrong with using water. Casein speeds up the process a lot and makes it easier to separate all of the different size particles.

I don't wash all of the casein off of the pigment. Once the pigment has settled at the bottom, I pour off the excess and let it dry so that there is a coating left behind. The casein serves to "deactivate" the pigment, since it has been known to react with linseed oil and darken.

This was based on research that found proteins in azurite samples taken from some early Dutch paintings. The blues in these paintings had not darkened at all and they wondered why this was the case.

If you are using tempera, this wouldn't be necessary.

Jules said...

As I'm using tempera and don't want the coating I assume that it would be easier if I don't use the casein at all rather than have to clean it from the pigment afterwards?

I've had a look at your other experiments with making colours. It's really informative seeing images of the process involved. For instance with the lapis lazuli all the books and blogs repeat Cennini's method but haven't actually tested it.

Zachary Kator said...

In that case, I would wash the color in water instead. With tempera you will get the purest blue color, without having to worry about it darkening like in oil paint.

Thanks for the comments!

Michael Price Pigment Workshops said...

Dear Zachary,
I published a paper in the Journal "Leonardo" (MIT press) on the levigation of azurite in a proteinacous solution in 2000. Kremer Pigments has been offering my preparation protocol for the mineral pigments levigated though casein since about 1998. Casein assists in the removal of impurities when the levigation is done correctly.
With best wishes,
Michael Price

Zachary Kator said...

Michael,

Thank you for the comments. I believe I have seen your pigments on the occasions that I have been to Kremer. I can appreciate the effort it takes to make them.

Zach