Harvey G. Stack, the patriarch of the family firm that calls itself the nation’s largest rare coin business, died

on Jan. 3 in New York. He was 93.

Mr. Stack joined Stack’s Rare Coins as a teenager in 1947, 14 years after his father and uncle had transformed what his great-grandfather had founded in 1858 as a foreign exchange house in Lower Manhattan into a dealership devoted exclusively to collectible currency.

Before retiring in 2009, he developed a standardized grading system for appraising coins, and he expanded demand among hobbyists by urging Congress to approve the U.S. Mint’s enormously popular 50 State Quarters Program which, beginning in 1999, honored each state with a commemorative coin in the order in which they had ratified the Constitution or were admitted to the union.

“History shows that rare coins of good quality have outperformed the Dow Jones industrials, real estate, and almost every other form of investment,” he said. But he counseled patience and pointed out that returns depended on two major factors: quality and rarity. What he looks for, he said, are coins that are “a little away from what a fellow can ordinarily find in his pocket or in mama’s shoe box.”