| Research: Selection of Crystals and Minerals |
© Michael Price Inc.
| Preparation Protocols for Mineral Pigments Technical details for the artist and restorer Azurite (blue copper carbonate) I usually prepare 10 to 14 grades of very pure azurite from approximately 10µm to over 100µm. The crushed and washed azurite is levigated two to three times through a casein solution according to the purity of the rock specimen. With azurite, the evenness of the pigment particle size in each grade is crucial to the end colour result. Layering with different particle sizes will result in different hues and tones of blue. Lapis lazuli Tests show a very pure lapis lazuli from the protocol I developed in 2004. The process is quite different from the method described by Chenino Cennini. I will reveal the method in a book I am working on in which all the protocols will be described in full detail. Malachite (green copper carbonate) Malachite is similarly sensitive to the acid in an oil binding medium, but the discoloration is not as noticeable as with azurite. Malachite is prepared in either a casein solution or diluted egg yolk solution according to the pigment particle size. Below 30µm it should be prepared in casein. With a particle size of 30µm to 80µm, an egg yolk solution of 1 part egg to 2 to 3 parts water can be used. There is a point in the dilution of the solution that the typical malachite green is instantly changed into a deeper and richer green. The change of hue is only minimal with a casein coating of the pigment particles. Orpiment, Realgar and Lead-Tin Yellow The unprepared pigments of either orpiment and realgar with lead-tin yellow will react chemically if mixed or come into direct contact with each other in a paint layer. I have been able to develop a layering of these yellows to produce a very powerful and luminous „middle“ yellow. The orpiment and realgar are both prepared in casein solutions and must be dried out for a minimum of one week before use. The lead tin yellow is soaked in a weak warm solution of rabbit skin glue size and allowed to dry for the same time before being mulled in either linseed or walnut oils. Cinnabar This mineral varies considerably in quality, but nevertheless, pigment of similar quality can be extracted. Preferably specimens such as the pieces of cinnabar (bottom right) should be used. The rock crushes quite easily and care should be taken not to turn it into fine powder too quickly. This will make it more difficult to remove impurities. Optimal levigation is in a weak casein solution. It will take a couple of days for the finest orange particles to settle out of solution. The finest pigment will give the most spectacular orange-red in a co- polymerized linseed oil. Vivianite and Purpurite Vivianite makes a fascinating pigment. After being crushed and ground it has to be levigated in a weak casein solution before being mulled in oil. Otherwise some discoloration in a paint layer will be evident after about five years. It separates easily into at least three grades from about 70-80µm down to a fine powder of 10-15µm. The fine powder as well as medium size particles of 40µm can be used as a glaze over malachite imparting a rich dark bluish hue to the layer of green. Purpurite, even of a low grade, produces a distinct rich and sometimes purplish brown which brings amazing luminosity to dark passages in a painting. No brown earth pigment can match its characteristics. |
Lapis lazuli
Malachite
Orpiment, Realgar and Yellow Ochre
Realgar and Cinnabar
Pyrolusite, Stibnite, Galena, Purpurite
and Vivianite
and Vivianite
Azurite
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