(1964-65) Blank Pattern - RB-5305, INCO

Coin Details

Description

Quarter-sized experimental blank RB-5305, the second entry in the RB-5300 composition group from INCO's Treasury evaluation program. Building on the baseline established by RB-5300, this blank incorporates a modified alloy formulation within the same general composition family. The progressive refinement visible across each five-unit increment demonstrates the iterative nature of metallurgical research: initial compositions established broad parameters, and subsequent variants fine-tuned specific properties to optimize performance. For the quarter denomination, optimization was driven heavily by electromagnetic requirements. The existing fleet of millions of vending machines, coin-operated telephones, parking meters, and transit turnstiles relied on sensing the specific electrical conductivity and magnetic permeability of 90% silver quarters to distinguish genuine coins from slugs. Any replacement alloy had to thread a remarkably narrow electromagnetic needle — different enough from silver in composition to be economically viable, yet similar enough in electrical properties to be accepted by existing coin mechanisms. The blank planchet stage of testing was when electromagnetic measurements were most reliably taken, as the uniform geometry of the unstruck blank eliminated variables introduced by the die design.

Rarity Notes

R-7 to R-8. Very limited production for technical evaluation, with most specimens remaining in institutional collections.

Cross References

RB-5305 (Robinson-Breen catalog). INCO experimental blank planchet series, quarter-sized, 1964-65.