"The most common and easily recognizable Akro Agate marble is the Corkscrew. This is a variegated-stream marble whose design is unique to Akro Agate. Two or more streams of colored glass were allowed to enter through the marble-making machine's shearing mechanism at the same time. Because the different colors were layered as they came out of the furnace and because the colors were of different densities, they created separate strata in the glass stream as it entered the shearing mechanism. Just before the shearing mechanism in the Akro machinery there was a small cup with a hole in the bottom. The glass stream entered the cup from the top and passed through the hole in the bottom into the shearing mechanism. If the cup was spinning, then a corkscrew was created. If the cup was not spinning, then a patch was created. The number of different colored spirals in the corkscrew, or the number of different color patches was determined by the number of nozzles that had glass flowing through them when the glass stream was created.

Corkscrews are identifiable as being two or more spirals of color that rotate around the marble from one pole to the other, but do not intersect. Different color combinations and designs were marketed by Akro Agate under a variety of names: Prize Name (two opaque colors), Special (three or more opaque colors), Ace (one opaque color and translucent milky white), Spiral (transparent clear base with colored spiral), Onyx (transparent color base with opaque white spiral). In addition, other names have been applied by children and collectors over the years: Snake (a Spiral or Onyx where the opaque or colored glass is on the surface and just below it), Ribbon (a Spiral or Onyx where the opaque or colored glass goes almost to the center of the marble), "Ades" (types of Aces with fluorescent base glass), and Popeye (a specific type of Special commonly found in Popeye marble boxes).

Two-colored white-based Prize Names are the most common corkscrew type. This is followed by two-colored color-based Prize Names, Onyx, Spirals, three-color Specials, Aces, four-color Specials, and five- color Specials. Although I have heard of six color corkscrews, I have never actually seen an example where the sixth color was not actually a blend of two of the other colors. If a true six-color Special exists, then it is extremely rare. Any corkscrew over 1" is extremely rare.

You should be very aware that the color and design combinations of corkscrews is almost limitless. You could easily amass a collection of several hundred corkscrews, of which no two would be the exact same color combination or pattern." -www.marblecollecting.com

(See an image of Akro Agate Corkscrews in the Marble ID Day article below)