Cartwheel Effect. A type of mint luster on a struck piece in which the flow marks appear as "spokes" from the center out to the rim; when the piece is tilted slightly the "spokes" appear to rotate as a wagon wheel, hence the name. Not all mint luster creates this effect, only that with strong striations (created by metal flow ) where the flow marks from the center outwards on the surface of the struck piece towards the rim.The effect is an optical illusion, but it is particularly desirable on coins and struck pieces because it is undeniable evidence that the piece is in original pristine mint condition. It is impossible to replace mint luster or the cartwheel effect after it has disappeared. Mint luster diminishes due to wear or tarnish as minute particles – dirt and grime, perspiration from hands, contact with any oily substance – fill the minute striations during the briefest handling. Thus it is an excellent test for true uncirculatedness.The cartwheel effect is never seen on full proof coins (which are polished to eliminate any flow marks). Thus it is a phenomenon of production run coins only. (Obviously it is not a characteristic of medals that are given a finish also eliminating flow marks.)See luster, reflectiveness.
excerpted with permission from
An Encyclopedia of Coin and Medal Technology
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor