The obvious answer is that somebody did not want the marble to roll anymore. That strikes me as sacrilegious, like permanently clipping the wings of a bird.
It then dawned upon me that this was not an act of vandalism, but a careful and deliberate act of veneration.
I call these marbles trophy agates. Their flat spot indicates special attention paid by its owner. It also proves these marbles were retired from active duty, but not thrown into a drawer and forgotten. Instead, they were modified to be displayed and admired, perhaps on a desk, workbench or mantle.
These were prized shooters and lucky marbles, some no doubt passed down from generation to generation. Their scars tell of countless battles fought, won, and lost. Most were likely trophies in the common sense of a prized memento; others were trophies from playing for keeps.
At some point in their history these cherished trophies lost their prominence. As their caretakers passed away, these marbles were tossed into junk drawers and shoe boxes, all but forgotten for decades, until they surfaced again in a family estate sale.
If you’re lucky you might find one of these tiny monuments. When I do, I place them on my mantle and restore them to their rightful place. If their owners had not vandalized them, I would never have known how special they were.
That’s not something you will hear a collector saying about any other type of marble.
In January, 1918, the Brick and Clay Record published an article on the Vitreous Clay Package Company of Ohio. It is a fascinating piece of American history, both for marble collectors and historians in general. Not only is it fascinating, but also it is quite an obscure bit of history, at least as measured by Google search results, for a search for "Vitreous Clay Package Company" yields only two or three results.
With so many American men still fighting "Kaiser Bill" overseas in World War I, labor was short. Imports of German marbles were blocked, making demand higher than ever. To meet that demand for marbles and other clay products, the Vitreous Clay Package Company employed women in a factory that could make up to five million glazed marbles and sixty thousand clay bottles per week.
In addition to photos of the actual factory and some of its equipment, the article goes on to describe in detail some of the methods used. I only wish they had printed close-up photos of the marbles themselves. I have to assume they were not thinking of the needs of marble collectors almost 100 years into the future!
Here are a few videos of amazing contemporary art glass marbles. It is difficult to do justice to these without having them "in hand" but thanks to higher resolution videos you can get a pretty good taste. Marbles of this quality can cost several hundred dollars, which considering their beauty of color and depth of construction, may be among the best deals in the art world.
The first is a marble made by Yoshinori Kondo of Japan.
An aptly named Universe Marble, by Gateson Recko:
This marble is a collaboration between Mike Gong (USA) and Rose Roads (Japan):
Finally here's a huge marble by Kenan Tiemeyer that appears to have embedded opal in it:
Where do you buy these? Vendors at marble shows often have them. Online you can buy many from Glass ORBits.
For the curious collectors, here is a close-up of the ducks in the circle.
This photo, as well as one of senator Lee S. Overman playing marbles with the same group of boys, are among countless other digital treasures in the Library of Congress Prints & Photographs Online Catalog.
Of special note in this marble collection are 70 sulphide figure marbles, many quite rare. An original sulphide marble box set will also be up for sale. Sulphide boxes are exceedingly rare and this one is expected to fetch between $4,000-$6,000.
As I always, I highly recommend you peruse the online catalog and feast your eyes on the excellent photography of these gorgeous marbles and marble box sets.
Update: Here is a video preview of the auction lots.