Question: I am concerned about my Mexican coins, which have high silver content and numismatic values. Do most coins with high silver content corrode in time? And if they become dark, will that affect their condition (grade) and value? How long does it usually take for a coin that contains about an ounce of triple-nine silver to corrode? I bought some airtight coin holders. Are these good at preventing such coins from corroding?--R.K.
Answer: Some coins will corrode--or rust--including copper pieces, but you will find that condition mostly in pieces that have been buried in soil or perhaps taken from a sunken ship. There's no question that coins will corrode when mishandled, wet or stored in a moist place. But the natural condition of coins darkening, an aging condition if you wish, is called toning. And to many collectors and professional numismatists, toned coins are actually more attractive and valuable than those considered brilliant uncirculated.
Toning gives coins a patina, and that discoloration can actually beautify a piece that otherwise might lack character. It can take years for a coin to darken, as you put it, but there is no specific time frame. Coins exposed to smog would probably tone at a different rate from coins kept in the desert. The toning or lack of toning will, indeed, influence a coin's value. All factors being equal, a toned coin will probably be worth more than one that is untoned.
As for airtight holders, they're designed to protect the coin in its present condition and inhibit the toning process. The leading grading services now provide such holders. The intention is that coins given a particular grade will be able to retain that grade in these safety holders, called slabs in the trade.
Q: Could you estimate the current value of the 1.9-ounce, 5-piece Singapore Year of the Rabbit set? I believe the amounts of gold are 1.0, 0.5, 0.25, 0.10 and 0.05 ounces to the set, and that only 10,000 sets were minted. I don't remember the year, but it was sometime in the 1980s.--R.C.S.
A: The 5-piece Singapore Year of the Rabbit gold sets are in the $800-to-$825 range.
Q: Please shed some light on the coin I am about to describe. This gold coin is about three-quarters of an inch in diameter. The head side bears a profile of a monarch. The raised motto states, "Edwardus VII D. G. Britt: Omn: Rex F:D: Ind: Imp:" The obverse has a helmeted horseman, horse rearing, sword in horseman's hand in the act of slaying a dragon. The date 1903 appears beneath this image. There is no denomination.--N.E.
A: You have described a British gold sovereign, which is essentially a bullion piece worth about $98.
One of the celebrated moments of history, the Mutiny on the Bounty, is marking its 200th anniversary and is being commemorated by the British Royal Mint for the Pitcairn Islands. The coin (pictured) will be struck in $1 sterling silver proof, $50 silver proof and 22-karat gold. The $50 silver weighs 5 troy ounces. The gold coins are $460 (2,500 mintage), the $50 silver is $110 (10,000 mintage) and the $1 silver is $44.95. Order from the British Royal Mint, P.O. Box 2570, Woodside, N.Y. 11377-9864; telephone (914) 677-6112.
Two thousand lots are listed in the massive Auction '89 sale July 7 and 8 in Chicago. Included is the finest known 1876-CC $5 gold piece, a rare 1927-S $20 gold piece (possibly the finest known) and a proof-68 1893 Morgan dollar, one of only 792 minted. Four firms participating in Auction '89 are Rare Coin Co. of America, Superior, David W. Akers and Stack's. Locally, catalogues are available from Superior, 9478 W. Olympic Blvd., Beverly Hills, Calif. 90212-4299; telephone (213) 203-9855.
Friday, Saturday and Sunday--The Newport Beach Coin Show and Auction is expected to draw bout 300 dealers this weekend and will be highlighted by a three-session auction beginning Friday at 7 p.m. and continuing Saturday at 2 and 7 p.m. Show hours are 10 a.m. to 7 p.m. Friday, 10 a.m. to 6 p.m. Saturday and 10 a.m. to 2 p.m. Sunday at the Irvine Hilton, 17900 Jamboree Blvd., Irving. Admission is $2. For information call (619) 273-3566.
Alpert cannot answer mail personally but will respond to numismatic questions of general interest in this column. Do not telephone. Write to Your Coins, You section, The Times, Times Mirror Square, Los Angeles 90053.