| Lapis Lazuli Used as a Pigment |
| Fragmentary illumination from a 15th c. Italian manuscript. Image taken from Recent Developments in the Conservation of Parchment Manuscripts. URL:http://aic.stanford.edu/conspec/bpg/annual/v15/bp15-14.html |
History
The vivid blue pigment that is extracted from the stone lapis lazuli was first introduced to Europe from Afghanistan as Ultramarinum, meaning beyond the sea. The lapis stone was ground into a fine powder creating the secret to ultramarine blue.
The first noted use of the stone as a pigment can be seen in sixth and seventh century AD cave paintings in Afghanistan temples where the stone was most predominantly mined. Lapis Lazuli ultramarine pigment has also been found in some Chinese paintings dating from the tenth and eleventh centuries AD and in a few Indian murals dating from the eleventh, twelfth and seventeenth centuries AD. Italian painters of the fourteenth through the fifteenth centuries AD used the brilliant ultramarine color to complement their vermilion and gold illuminated manuscripts and panel paintings.
Painters of the Renaissance had a strong affinity for the ultramarine pigment
due to its vivid rich consistency. Because of the costly manner by which the pigment is extracted from the stone lapis lazuli, natural ultramarine blue has been one of the most costly and precious of the artist materials equaling and sometimes exceeding the price of gold. Artists used the pigment quite sparingly reserving its use for the robes of the Virgin Mary and Christ child.
| Madona del Granduca.c. 1595 by Raphael. Scanned photograph taken from, The History of Art Fifth Edition, Janson (1995) |
Natural ultramarine pigment is extremely difficult to buy at the present and is only available in England occasionally, the price often exceeding its weight in gold. Most painters wishing to obtain the pigment must purchase the stone from a gem dealer and extract the pigment themselves.
Extraction of the pigment
Natural ultramarine blue made from lapis lazuli is one of the most difficult
pigments to extract through grinding by hand. Only the highest quality
of lapis having a higher percentage of lazurite with only small amounts
of impurities is sufficient for pulling a rich blue. The normal grinding
and washing technique used to extract other pigments will only produce
a pale grayish blue powder. An improved method for extracting
the blue pigment was developed in the 13th century. The process consisted
of mixing the ground lapis lazuli stone with melted wax, resins, and oils,
then wrapping the mixture within cloth and kneading it under a dilute lye
solution of potassium carbonate (
Miller & Alquist, 1998).
This
process resulted in the blue particles collecting at the bottom of a holding
vessel, while most of the impurities as well as the colorless crystals
remain within the mass of wax, resin and oil. The process
is performed three times, each successive extraction creating a lower quality
pigment. The third and final extraction results in a predominantly
colorless material having only a few blue particles, creating what is known
as ultramarine ash, used as a glaze due to its pale blue transparency.
A much less costly and time consuming alternative to natural ultramarine pigment is synthetic ultramarine blue which is easily obtained at the present. Synthetic ultramarine is produced today by heating clay, soda, sulfur, and coal in furnaces. Unfortunately synthetic ultramarine is not as vivid a blue or as permanent as the natural version. The particles within synthetic ultramarine are much smaller and uniform than natural ultramarine thus diffusing the light more evenly.
Chemical aspects of the pigment
Natural ultramarine is one of the most complex mineral pigments. It is a complex sulfur containing sodium silicate, basically a mineralized limestone containing the blue cubic mineral called lazurite (Miller & Alquist, 1998).
The following are the chemical properties of natural ultramarine
(Miller & Alquist, 1998):
| unaffected by heating up to redness |
| unaffected by ammonia or caustic alkalis |
| unaffected by sodium hydroxide |
| unreacive with base chemicals |
| extremely susceptible to even the most minute and diluted mineral acids and acid vapors; because of this susceptibility natural ultramarine pigment was never used in frescoes |
| the pigment is almost entirely permanent and highly stable in light |
Binders used to hold the pigment
The vivid blue color of the natural ultramarine pigment may only be maintained within aqueous solutions, gum Arabic and egg tempera. Oil based solutions are less favorable due to a low refractive index leading to a dark blue color and a highly viscous and stringy consistency rather than vivid brilliant blue when applied in thick layers. The most favorable results with oil based solutions are when a white pigment is added producing a brilliant opaque blue ( Miller & Alquist, 1998).
To produce a usable ultramarine oil paint mix: 2.0 g of extracted natural ultramarine pigment with approximately 2.25 ml of linseed oil. To create a watercolor paint mix: 1.0g of pigment with 20 drops of a gum arabic solution which includes (gum arabic, honey, glycerin, and sodium benzoate) plus a little water to dissolve the solution to apply the paint. A functional egg tempera may be produced by adding 2.0 g of pigment with equal parts egg yoke (Miller & Alquist, 1998).
The material for this section came primarily from:
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