Posted 10/27/2009 11:19 pm
Jeff 11 Pictures would be nice, but you have made a few interesting observations which warrant comment.
That is essentially the correct weight since the silver issues were 7.77 grams and the CN issues were essentially identical in weight. This identical weight was critical in the 1950s because most coin operated devices at that time had simple weighing devices. So most replacement CN coins matched the silver coins they replaced in weight.
But you say the other coin is:
If it is EXACTLY the same size you can make a ratio to approximate the Specific Gravity. The underweight coin is 72% of the weight of CN. Copper and nickel have SGs near 8.90 for Ni and 8.96 for Cu. So a mixture CN could be called 8.93 safely. Seventy two percent of that is 6.4. Antimony is 6.69 and is a metal often used in forgery. That is a fairly close match given the method of calculation.
Antimony is a common metal and inexpensive. It was a by product of silver mining and has been known since Egyptian times. It is used as an alloy to harden lead. Today it is used in electronics as an insulator. The hardness of pure Antimony is about the same as silver (3.0 on the Mohs scale). It is a dark gray in color.
The only problem I see here is the comment that it is "softer". Now if you meant it has a slippery or greasy feeling to it, then Zinc is a good candidate and with an SG near 7.1 it is also a decent match and only a slight variation in thickness would produce a match.
Both zinc and Antimony and various alloys including lead were used in the 1950s and 1960s by forgers making copies of common silver coins for circulation. These are typically cast in transfer molds. I own numerous types but consider them all to be of very minimal value. The Antimony copies can sometimes be snapped in half fairly easily if the metal is near pure. Antimony is brittle.
Zinc coins are noted for surface blooms (spots on the surface) and for their rapid corrosion in wet environments. Both zinc and antimony have the advantage of fairly low melting points so casting with them is easy.
Pot metals (a generic group of alloys) are the most likely candidates for your coin. Typical forgeries are referred to as Pot metal or White metal.
So you have a coin worth looking at, but as a counterfeit it is not likely to be of great value except to teach others what to look for.
Quote:
One is the standard Copper-Nickel, and weighs 7.8 grams.
One is the standard Copper-Nickel, and weighs 7.8 grams.
That is essentially the correct weight since the silver issues were 7.77 grams and the CN issues were essentially identical in weight. This identical weight was critical in the 1950s because most coin operated devices at that time had simple weighing devices. So most replacement CN coins matched the silver coins they replaced in weight.
But you say the other coin is:
Quote:
Exact same diameter, and appears to be same thickness - but weighs 5.64 grams and is made of a much softer metal much darker in appearance
Exact same diameter, and appears to be same thickness - but weighs 5.64 grams and is made of a much softer metal much darker in appearance
If it is EXACTLY the same size you can make a ratio to approximate the Specific Gravity. The underweight coin is 72% of the weight of CN. Copper and nickel have SGs near 8.90 for Ni and 8.96 for Cu. So a mixture CN could be called 8.93 safely. Seventy two percent of that is 6.4. Antimony is 6.69 and is a metal often used in forgery. That is a fairly close match given the method of calculation.
Antimony is a common metal and inexpensive. It was a by product of silver mining and has been known since Egyptian times. It is used as an alloy to harden lead. Today it is used in electronics as an insulator. The hardness of pure Antimony is about the same as silver (3.0 on the Mohs scale). It is a dark gray in color.
The only problem I see here is the comment that it is "softer". Now if you meant it has a slippery or greasy feeling to it, then Zinc is a good candidate and with an SG near 7.1 it is also a decent match and only a slight variation in thickness would produce a match.
Both zinc and Antimony and various alloys including lead were used in the 1950s and 1960s by forgers making copies of common silver coins for circulation. These are typically cast in transfer molds. I own numerous types but consider them all to be of very minimal value. The Antimony copies can sometimes be snapped in half fairly easily if the metal is near pure. Antimony is brittle.
Zinc coins are noted for surface blooms (spots on the surface) and for their rapid corrosion in wet environments. Both zinc and antimony have the advantage of fairly low melting points so casting with them is easy.
Pot metals (a generic group of alloys) are the most likely candidates for your coin. Typical forgeries are referred to as Pot metal or White metal.
So you have a coin worth looking at, but as a counterfeit it is not likely to be of great value except to teach others what to look for.
