Dioxazine Violet is transparent and has very high tinting strength. It is a staining pigment, very dark valued when it is used at full strength. Concentrated, it paints out nearly black, but it mixes with Titanium White to form bright, opaque tints of purple. PV23 produces slightly redder shades than PV37. Because the hue can vary with the conditions of preparation and grinding, it may be offered in red shade, blue shade, and so forth.
Dioxazine Violet has good lightfastness. There may be some concern about it fading or shifting in color in tints and washes. Some artists have reported that PV37, a molecular variant, is more lightfast than PV23.
Two molecular variants of Dioxazine Violet, PV23 and PV37, are available. They have similar properties, but mix slightly differently.
Calcium carbonate, the mineral constituent of chalk, is a low tinting strength, inexpensive white pigment that is often used is a buffer and filler. Because of its low tinting strength, it is overwhelmed by other colors. It is used in gesso and other coatings to give the surface more tooth, a desirable characteristic for some painting techniques.
Calcium carbonate is lightfast. Like all carbonates, it reacts with strong acids
Calcium carbonate is completely non-toxic, and is used in many food, cosmetic, and pharmaceutical products. However, excessive consumption is not recommended.
Naturally occuring chalk deposits have been mined since prehistoric times. Rocks and minerals that contain calcium carbonate include aragonite, calcite, vaterite, chalk, limestone. marble, and travertine. Calcium carbonate is the principle component of lime, used in many agricultural and industrial applications.
cadmium sulfide and cadmium selenide
CdS x CdSe
Cadmium Red is a bright, warm red that ranges in shade from orange-red to maroon and is available in light, medium, and dark versions. It is strong and opaque, with good tinting strength. Cadmium Red dries slowly. It grays down when mixed with white, mixes well with blues to create a range of browns, and mixes well with Cadmium Yellow to create a strong orange. It also works well in neutral mixes. Cadmium pigments have been partially replaced by azo pigments, which are similar in lightfastness to the cadmium colors, cheaper, and non-toxic. Hues vary by brand. Cadmium Red is usually available in either a pure grade or a cadmium-barium mix. The cadmium-barium mix has the same permanence as pure Cadmium Red, but it has a lower tinting strength.
Cadmium Red is lightfast and permanent in most forms, but like many cadmium pigments, it will fade in fresco or mural painting. Its improved lightfastness has helped it to replace Vermilion on the artist’s palette.
Cadmium Red is a known human carcinogen. It is extremely toxic if inhaled and slightly toxic if ingested.
Cadmiums get their names from the Latin word cadmia meaning zinc ore calamine, and the Greek word kadmeia, meaning Cadmean earth, first found near Thebes, the city founded by the Phoenician prince Cadmus. Metallic cadmium was discovered in 1817 by Friedrich Strohmeyer, but Cadmium Red was not introduced until 1907 in Germany.