Wednesday, October 20, 2010

Ultramarine, Part II

Natural Lapis lazuli is a beautiful stone , but in raw form a mediocre pigment. As I covered in the first installment lapis lazuli is not homogeneous. The brilliant blue color comes from lazurite, the other constituent elements being impurities. Only the very highest quality stones create a rich blue when crushed into a pigment. For centuries artists and craftsman had to make the best of the dull, ashy blue that was often a result.

A comparison of different grades of Lapis Lazuli.

Then sometime around the 13th century, alchemists developed methods to extract lazurite from its impurities. This involved adding the pigment into a melted pastiche of wax, resins, and linseed oil. The resulting blob of material was kneaded in a solution of water or weak lye. The pure pigment was released and could be collected. The work was time consuming and came at a huge expense.

Many recipes along these lines still exist. Among these, the most detailed was written by the artist Cennino Cennini in the early 15th Century. His book, Il libro dell'arte, or The Craftsman's Handbook is a charming guide to how art was made during the Renaissance. A whole chapter is devoted to pigments, including a very detailed recipe for lapis.

Cennini's describes a "plastic" to be made from beeswax, mastic, and pine resin. He calls for one pound of lapis powder to be used in the recipe. I had a lot less, so I adjusted each quantity accordingly.

Once I weighed out each ingredient, they were melted together in a saucepan.

I poured the plastic into a bowl, then added my lapis powder. I proceeded to knead the still liquid plastic until the lapis was evenly dispersed. Like kneading bread dough, one must cover ones hands with something so it does not stick. In this case Cennini says to use linseed oil, instead of flour. The plastic cooled quickly and began to form a soft, solid ball.

I let the plastic sit for 3 days, per Cennini's instructions. Each day I took it out and kneaded it again.

After this time had passed the plastic was placed in a bowl pull of warm dilute lye and kneaded again like bread. Because lye is caustic, I took precautions to protect myself. Cennini recommends using two round sticks while handling it in the lye. I used two chopsticks.

While kneading the plastic, the pure lazurite should gradually be released. Once it has settled on the bottom, the plastic can be removed, and the lye poured off from the fresh pigment. The first extraction is the purest and finest. Cennini recommends using fresh lye to repeat the process again in a new bowl. This will continue until all of the blue has been extracted from the plastic, and it becomes worthless.

I consider my attempt a partial success. While I was able to obtain some very fine pigment, the plastic began disintegrating in the lye almost immediately. I was not able to repeat the process many times, as Cennini recommends. A lot of small pieces of wax and resin ended up in the pigment, and will have to be removed somehow before it can be put to use.

I will need to do more research before I try this method again with my finest lapis.


Jules said...

I'm really glad to have chanced upon your experiment with Cennini's method. I have bought some lapis lazuli slabs to make pigment with and was planning to try this method. Did you heat the lapis lazuli prior to crushing it? I've been told that it makes it easier to crush but I haven't tried it yet. Have you had another go at this process? Have you been able to remove the wax from your pigment?

Zachary Kator said...


Lapis really is beautiful isn't it?

I haven't tried heating the rock before crushing it, but I imagine it probably works just fine.

I haven't had another go at the Cennini recipe yet. I get the feeling something is missing from it. For instance, later on I discovered that what we call lye today and what they probably used in his time are different chemicals.

I used a little unpurified lapis on my last painting just for fun. I thought the color was not bad at all. The lapis I used was above average though.

Jules said...

I love the stone.

I think that I'm going to try levigating it for now. The stones I've got don't have any obvious calcite and are a very intense blue. I could always purify it later.

I assumed that lye has always been made from wood ash.

We use lime or poplar quarter sawn-boards for panel icons. I've bought a 19 inch wide quarter-sawn kiln-dried piece of oak panel but I've been told that with large boards the oak tends to split after being gessoed as it dries out much quicker at the exposed edges.

Zachary Kator said...

I hadn't heard that, but it wouldn't surprise me. It hasn't been easy to find information on building panels. Most of what I've learned has been from trial and error.

Most artists I know are perfectly happy using MDF and masonite anyway.

Jules said...

My tutor has sent me a recent research paper on natural pigments that has an alternative recipe for extracting ultramarine from lapis lazuli. It has more detailed instructions about the strength of the lye to be used and more ingredients for making the plastic. Also it describes how to heat the stone before hand. If you would like a copy of the document I will email you it. I'll need an email address to do so.

attila said...

use weaker solution of potassium carbonate and quite hot for extraction

use rubber glover

that way you can keep plastic mass together

Zachary Kator said...

Thanks for the comment. I'm going to try this experiment over again very soon, and try to apply everyone's helpful suggestions.

Antonia di Lorenzo said...

Zachary and Jules: there is some really excellent info on panel construction on this site, where you can download the symposium notes on conservation of panel paintings. Parts 1 and 2 are useful for info on original construction, 3 & 4 deal only with conservation aspects. I've found museum conservator notes in general a good source of info on techniques and materials

Wazza Beckham said...

Where did you all buy Lapis rocks from without havung to go to Afghanistan then? I live in Britain and the only place I can find it is as a pigment which is very pricey. There's also one from China but the quality isn't supposed to be very good.

Zachary Kator said...

Worst comes to worst I've had surprisingly good luck finding things on line, if you can find a reputable seller. I would try buying in small quantities first, and if you like the quality, you can always purchase more. Also, if you're willing to purify the Lapis, better quality pigment can be made from cheaper stones.

luis aguirre said...

hi Jules, excuse me, do you have the paper about lapislazuli, yet? i apreciate it, my mail is thank you so much. luis aguirre

luis aguirre said...

hi Jules, excuse me, do you have the paper about lapislazuli, yet? i apreciate it, my mail is thank you so much. luis aguirre

luis aguirre said...

hi Jules, excuse me, do you have the paper about lapislazuli, yet? i apreciate it, my mail is thank you so much. luis aguirre

sid said...

can i got that paper ?
i have extracted blue pigment. but my mass is so hard. dont know how to make it soft.