Lapis Lazuli extraction - Fra Angelino natural ultramarine recipeApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2017-10-13 10:35:14 ...
Most recent comment 2017-10-13 12:06:29
Do you have an exact recipe for extracting Fra Angelico blue from lapis lazuli? A student of mine needs the recipe for his conservation degree, but his professor also wants more scientific quantities. Cennino cennini's recipe for natural ultramarine is too vague for their MA classroom. Ex: how strong should the lye solution be and it's ideal ph? How much ashes to water? How much lazuli to resin, wax and oil? Etc. Thanks
Answers and Comments
I am first very surprised that any conservation professor
would ask for such specifics due to the vagueness of the original recipe. I
have tried to reconstruct Cennini a number of times and it is very difficult to
get satisfactory results. Many years ago I asked a similar question on
the site that this forum is inspired, AMIEN and I was
unable to find anyone who could give me the info that you seek.
Kremer Pigments has this down but I have asked a couple of
times and they are reluctant to give it out their procedure. There are many
variables and the short answer is that I have not worked out a system but have
achieved satisfactory result using a simplified version.
First, you need to select the purest and deepest pieces of
lapis. Remove any obvious impurities first, then crush and again remove any
impurities. You can heat the stone to a high temp and quench in water where it
will break into much smaller pieces. I tried this but ended up pounding and
crushing in a mortar and pestle. Then grind the powder to a mid-coarse powder
(something like 50 micron or so). You will need a series of sifting screens. It
is still an enormous amount of work to hand grind the powder to even this
moderate degree of fineness. Access to a mill would make this so much easier. I
have then melted together something like 1 part beeswax, 3 parts rosin, and 2
parts mastic resin. This mixture is the 1 part by volume. To this I added about an
equal volumetric amount of powdered lapis and heated and stirred all together. I
did not add any oil like suggested. This was then poured out onto a piece of
mylar. My previous attempts at this process ended up saponifying the oil in the
alkaline water solution and complicated the process. Probably my pH was too
I made balls of this after it cooled. I then let them age
for a couple of weeks. I them put them in little scraps of artist’s linen. I
made up a number of basins of water (maybe a quart apiece) to which I added a tablespoon
or so of potassium carbonate (the lye of Cenneni’s time as opposed to caustic
lye which is sodium or potassium hydroxide). I did not add oil to my hands but
used nitrile gloves other than that I followed the remaining extraction process
mention in Cennini.
My result were visibly purer ultramarine but the yield was
rather low and the extraction process took a very length period of time.
In the long run, I am not sure that anything that I provided
here will be of any help. I had many frustrating attempts to carefully follow
the recipe in the distant past but my failures dissuaded me from taking precise
notes even though I would appreciate having them today. My attempts also uses
some modern materials like mylar and omits others like the use of oil. This is
the best that I can do.
Just so you know, there are later recipes for the extraction
of ultramarine. You can probably references that contain them by doing a search
on Art and Archeological Technical Abstracts. Some are clearly influenced by
the Cennini recipe but others are a different take on the process. I am sorry
that I could not be of more help.
Please let us know if you do find a modern recipe that adds
precise measurements and pH to the Cennini recipe.
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