Collecting marbles is a game, and the person with the greatest skill is the winner. Winning at marble collecting requires practice and knowledge and is not child's play. Identifying rare marbles requires playing with the big boys by reading their books, attending marble shows and shopping where you can engage in conversation with collectors with knowledge.
Some basic knowledge can get you started collecting rare marbles, but building on the basics will keep your interest and broaden the potential for developing a valuable collection, since rarity is a value factor along with size and condition.
Learn some general information for collecting marbles. Not all marbles are glass, so recognise crockery, Benningtons, stoneware, china, agates and even wooden marbles. Glass marbles are handmade or machine made, and may be old sulphides with figurines in the centre, or may be imports from Mexico or China. The knowledge of rarity and value is what builds a quality marble collection.
Watch for unusual sizes of marbles. Two inches and larger and one-half inch or less are sizes that may make an ordinary marble a rare one. Bennington pottery marbles are brown or blue or a combination of brown and blue, and are common in small sizes. Robert Block considers Benningtons over two inches in diameter as too rare to value, and crockery marbles over two inches as non-existent.
Look for single pontil handmade art glass marbles, as these marbles were at the top of the cane, and there was only one for each cane that produced several marbles with two pontil marks.
Collect matching pairs or twins. Find handmade marbles that likely came from the same cane. After many years of trading and playing for keeps, pairs of marbles are uncommon. Even rarer are large marbles from the same cane. Mike Adams wrote about twins found in recent years: "The rarity is off the charts."
Find marbles in the original box, in a game or with the original bag. Marble accessories help date the marbles and sometimes identify them, so they have historical and monetary value. Marbles with original accessories are rarer and have added value.
Look for artistic merit and little damage. Bright colours in controlled designs are rarer and more desirable than muddy colours with seediness, or tiny bubbles throughout the glass.
Damage is common in marbles, since they were toys. Check damage with a magnifying glass or loupe, as there may be internal fractures and eyelashes or half moon fractures not easily seen. Consider size and condition as well as scarcity to identify rare marbles.