Color zoning

Color Zoning & Pleochroism in Ruby
Color zoning is a phenomenon caused by overlapping growth layers as the corundum crystal is formed.

Color Zoning
Uneven color in gemstones in irregular patches. Can be either different colors or different tones of the same color.
Colored Stones
A gemstone other than a diamond.

color zoning Color patches that has been noted in synthetic blue diamond but does occur in natural diamonds. A term commonly used in colored stones.
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Color zoning, inclusions, dichroism need attention. Rectangular step-cut stones cut with the table parallel to c-axis in deeply colored stones often have steep pavilion facets at the ends of the rectangle to minimize the deep color parallel to c.

Color zoning lines are commonly poorly defined in heat-treated stones. Other characteristics include features like cross-hatched color zoning and sharply defined cloudy layers or patches.

COLOR ZONING - Uneven color distribution in a gem material appearing as irregular patches of varying colors or different tones of the same color.

Color zoning - Patches of uneven color in colored stones that detract from pure dispersion and uniformity of color.
Comfort fit - A term for ring design where the edges are smoothed to a round surface for maximum comfort.

Color zoning can also reduce color coverage. Ideally, no zoning should be present. Moderate to severe color zoning does impact quality, and thus price.

Zoning (color zoning) A term that describes the uneven distribution of color in a gemstone. Zoning is best seen when looking at the stone through the top table facet.

Color zoning in Jagdalek rubies is extremely sharp and narrow, forming in the typical hexagonal pattern when viewed parallel to the c axis. The most distinctive feature of Jagdalek rubies are the small spots or zones of a sapphire-blue color.

Colors: Colorless, pale green, yellowish green, yellow shades, bluish green, green, rose, violet, color zoning
Luster: Vitreous
Hardness:3.5
Specific gravity: 4.32-4.48
Cleavage: Good in one direction,fracture conchoidal to uneven
Refractive index: 1.

banding The presence color zoning lines, or "bands", in some minerals.

Fall 1975, Color zoning in an emerald, p. 73, 2pp.
Summer 1976, Included rutile needles in emerald, p. 174, 1p.
Fall 1976, A quartz crystal inclusion in Colombian emerald, p. 213, 1p. (See also Summer 1977, p. 314, 1p.) ...

The most valuable blue sapphires have the color of an intense blue without color zoning and internal flaws. Color zoning refers to variation of intensity within the stone, exhibiting deeper blue hues while other areas in the stone may appear lighter.

They lack the color zoning so prevalent in other sapphires, their uniform "corn-flower blue" color is natural (not the result of heat-treating), and their clarity is uniformly high. These features rank them among the world's finest sapphires.

By the late 1980's, a second-wave of lattice-diffused stones appeared, with just a little color added on already blue stones with color zoning problems (Hughes, 1988, 1991, 1992).

AAA Dark, clean, little or no color zoning, good cut.
AA Medium dark, clean, little or no color zoning, good cut.
A Medium light, clean, little or no color zoning, good cut.

1) a: Diffused brightfield lighting is best for this, as it can reveal color zoning and growth patterns that might indicate synthetic origin, or unusual concentrations of color that might indicate dyeing or diffusion.

Phantom - A crystal which shows an internal image of a crystal, caused by color zoning or inclusions
Phosphates - Minerals containing the phosphate (PO4) radical as a major component. (Apatite) ...

Take time to observe well from every angle the gems presented and look for defects (color badly distributed, color zoning too present, too apparent inclusions, cutting defects, etc).
This time of observation can be used for reflexion or calculation.

It is important that the color within the stone be evenly distributed so that no "color zoning" becomes too apparent. Heavily zoned or included cabochon sapphires will cost a lot less than clean transparent cabochons.

texture In transparent gems, a description of color zoning visible face up. In pearls, a reference to any indentations or imperfections in the pearl's surface.
tint A hint of color, not sufficiently saturated to be a hue.

Any color zoning or inclusions diminish the price. Generally, amethyst from South America tends to be available in larger sizes than African amethyst but amethyst from Africa has the reputation for having better, more saturated, color in small sizes.

They often display intense color zoning with outlines being darker in tone. Unlike Kashmiri and Burmese varieties Sapphires recovered from Kanchanaburi are mostly of commercial quality forming the part of precious sapphire jewelry pieces.

Citrine - Mohs Hardness: 7 - Treatment: usually heat treated - Color: Medium to dark gold; some color zoning (See also Quartz) Is the yellow or golden yellow variety of quartz.

See also: Color, Stone, Gemstone, Cut, Crystal