GOLDEN Artist colours produces a large assortment of products that impart shimmering iridescent or interference reflective qualities. This Information Sheet discusses what these paints are and how the artist can incorporate them into an artwork.

Product Description

The GOLDEN Iridescent and Interference colours achieve their reflective properties by synthetically reproducing several natural phenomena-the nacreous, or pearlescent, qualities found in fish scales or the dust of a butterfly's wing, and the shiny and reflective qualities found in certain metals and minerals.

"Coarse" Iridescent and Interference colours are simply larger particle size versions of the "Fine" Iridescent and Interference products. Coarse colours in the Iridescent line include Copper, Copper Light, Gold and Pearl. The Coarse Interference colours are Blue, Gold, Green and Red.

All of GOLDEN's Iridescent colours produce a luster quality by themselves, or when mixed with other colours and mediums. The GOLDEN line of Iridescents can be separated into 3 groups based on chemical composition.

Group I: These colours are derived from mica platelets. They are then coated with an extremely thin layer of titanium dioxide. Refraction and reflection of light at the titanium dioxide layers produces various colours and pearlescent effects. Group I pigments include:

• Interference colours
• Iridescent Pearl (Coarse and Fine)
• Silver

Group II: These colours are also derived from mica platelets, but an iron oxide coating causes Group II pigments to possess hues in addition to pearlescent qualities. This group includes:

• Iridescent Gold (Coarse and Fine)
• Iridescent Copper and Copper Light (Coarse and Fine)
• Iridescent Bronze

Group III: A third group consists of reflective colourants that do not fit the above descriptions, including highly metallic pigments:

• Stainless Steel (Coarse & Fine)
• Micaceous Iron Oxide
• Mica Flakes (all varieties)
• Luster Arises from Layers of Pigments:

The pigments in the first two groups (non-metallics) are composed of very thin, highly reflective and transparent platelets. Although the pigments themselves are transparent, the optical illusion of colour is produced by the multiple reflection of light between microscopic layers.

The Phenomenon of Light Interference:
The property at work in the Interference colours is known as light interference, most commonly seen in the rainbow effect created by a thin layer of oil on the surface of water. Thomas Young identified this phenomenon in 1801 in a series of investigations that were eventually instrumental in advancing the theory for the wave-like nature of light.

Whenever light strikes a boundary between two materials of different densities, the light will either be reflected or refracted. If the refracted light encounters yet another boundary between materials of different densities, this light will again either be reflected or refracted. This process continues every time a new phase is encountered.

Light interference results from these concurrent multiple reflections and refractions of light. If the interference is constructive in nature, a strong colour stimulus results. With Interference colours, a specific thickness of the titanium dioxide (TiO2) layer allows only a narrow spectrum of colour to be reflected in phase, while all other reflected colours undergo destructive interference and are not observed. Since these pigments are transparent, a portion of the light will be transmitted and the resulting colour will appear as the compliment to the reflected colour.

Excellent Weathering Resistance:
Mica is quite insoluble in strong acids or bases, is inherently lightfast, and remains unaffected by water. When combined with a 100% acrylic medium, mica yields very stable paints that offer excellent permanency.

Mica's chemical and UV resistance properties distinguish the Iridescent Mediums from most metal pigments, such as coppers, bronzes and even aluminum flakes. Metals have a tendency to rust or corrode as they continually oxidize over time. With the Iridescent colours, all components are already in the most stable state of oxidation, and there is no possibility for change resulting from further oxidizing reactions.

The metals that GOLDEN has chosen to offer are known to demonstrate remarkable durability. GOLDEN Stainless Steel (Coarse & Fine), which consists of extremely durable 316L grade stainless, is very resistant to salt spray and acid spotting, as well as alkaline cleaners or detergents. The Micaceous Iron Oxide, although highly reflective, is not in a metallic state but is already oxidized.
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Product Application

Maintaining Bright Surfaces: The Options.

The highly reflective flake pigments used to produce Iridescent Mediums are extremely thin. These platelet pigments range from 1 to 2 microns in thickness, and up to 90 microns in diameter for the Fine and 180 microns for the Coarse. Consider that the surface of an average flake of Iridescent Pearl could carry over 50,000 Carbon Black pigment particles placed side by side. Due to the larger particle size and the transparent nature of mica, iridescent colours tend to be less potent than other acrylic formulations.

Although no rule is absolute, some procedures for maintaining bright surfaces have proven their effectiveness. What follows is a brief review of some of the more successful approaches.

• To produce the brightest colours with the Interference line, add a very small amount of black-1:100 or less. The black will strengthen the reflected colour. Add more black if darker colours are required.
• To maintain the brightest possible effects with Iridescent colours, avoid mixing them with opaque colours.
• Be aware that blends made with matte materials such as matte mediums and matte gels will also reduce iridescent qualities by scattering the light that hits the surface. Adding gloss materials, such as GOLDEN Gloss Gel, increases interference qualities by heightening reflectivity. The addition of Gloss Gels and Mediums also provides better spacing between pigment particles, maximizing the effectiveness of each reflective pigment.
• Overall, thicker applications will cloud the paint and weaken the intensity of the Interference colours. Thinner applications increase the interference qualities. As the level of dilution increases, the pasty look disappears. Applying thin layers, whether by wash or glaze, effectively forces particles to lay flat with the large broad side facing the viewer. As more particle surfaces are exposed, the shimmer or luster increases.

Other Techniques and Considerations:
Since the Iridescent and Interference colours are relatively transparent, it is important to consider the impact of the base coat. By varying the colour of the base coat, the overall colour effect can be varied dramatically, especially when the Iridescent or Interference layer is applied transparently. For example, Interference Blue can be applied in glaze form over a light yellow or a dark red to yield some unique effects. Relatively transparent colours can be wet-blended into the Iridescent or Interference colours to produce other interesting results. Combining additional colours and Gloss Gels and Mediums can create some exciting glazes, in thin or thick films.

The important thing to remember about the Iridescent and Interference colours is not to take them at face value. They can provide a range of colours and effects never before available, and many of their uses have yet to be discovered.
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