Recently, there have been several hologram coins released by some major mints. Other coins have had holograms added after their release. And they can add a beauty that changes as you hold the coin in your hand, giving a multitude of exciting, changing colors.
Holograms, as they apply to coins, are having the coins appear to be three dimensional by coating a portion of the coins. It appears a clear coating produces the desired result. A clear coating over a selective portion of the reverse makes that portion of the obverse to appear to have depth.
The easiest way to describe what is happening is to understand why gasoline can appear to make a rainbow of colors when it is spilled, especially if it is floating on water. Light waves are very short. When light passes through a thin film and reflects off the other side, or bottom of a gasoline layer, the light may have multiple reflections within the thin layer. Some light might also reflect off the top of the layer. The light that one sees in a combination of light that reflected from the gasoline and light that went through the gasoline layer, perhaps several times, and emerged again. If the waves come together such that they are in phase for one color, they will not be in phase for other colors. That reinforced wavelength gives the layer its color.
In the case of hologram coins, the coin itself is often gold or silver, with a highly reflective surface. So the reflection of the light that goes through the thin layer is even more likely, since the light cannot pass into the coin in any appreciable amount. As a result, the coin flashes the color that is reinforced due to reflections. But coins change color. This is explained by the fact that light travels a different distance through the hologram when the coin is held at one angle than if it is held at another. A slight difference in the optical path when one is talking about wavelengths of light is enough to completely change the color that is reinforced. Any movement of the coin when held, or any change in position when viewing a hologram coin, can cause the coin to completely change its color scheme.
When purchasing a hologram coins, first determine the quality of the hologram. Generally, it is better to have the hologram added at the mint during the minting process than to have a coin that had the hologram added later. If the hologram is added in the minting process it is less likely the hologram will detach from the coin. Another reason is coin collectors prefer, in general, to have their coins as close to the state the coins were when they left the mint as possible. Altered coins do not command the same value as similar coins minted with the desired addition of a hologram.
The Royal Canadian Mint has had several series of hologram coins over recent years. Some have a small hologram on them, others have a large portion of the reverse covered with the hologram. Perhaps the Natural Wonders Collection of silver twenty dollar coins is most impressive. The twenty dollar Canadian Architectural Collection is also impressive. And the Canadian Maple Leaf holograms are beautiful.
The Royal Australian Mint has had hologram coins in the past, and are once again offering a hologram coin depicting the Aurora Australis.
The Perth Mint offers a hologram coin, but it is one of the Royal Canadian Mint's Tall Ships Series. The Tall Ships Series in another popular Canadian series.
Less impressive is the Canadian Loon and the Canadian Transportation Series. And the Canadian Maple Leaf holograms are beautiful.
At Black Spaniel Gallery, hologram coins are considered highly desirable. Go to http://blackspanielgallery.8m.com for a link to many major mints in English Speaking countries, including all of those mentioned in this article.
If you plan to add hologram coins to your collection consider those from the quality mints. Henry M. Smith provides information and sells coins through Black Spaniel Gallery. The website is http://blackspanielgallery.8m.com for both coins and information.
The author, in addition to being involved in coins, is an assistant professor of physics.
Article Source:
http://EzineArticles.com/?expert=Henry_M._Smith
