"The only substances ever declared as money within the U.S. were gold and silver, in coin form, with copper/nickel serving in token capacity only. See: 12 USCA 152 re. "lawful money" and Coinage Act of April 2, 1792, at Sections 11, 16, & 20; re. copper/nickel tokens, see Sec. 9, and 31 USCA 460."
Original U.S. Constitution
Art. I Sec. 8 Cl. 5
[Congress shall have Power ...] To coin Money, regulate the Value thereof, and of foreign Coin, ...;
Art. I Sec. 10 Cl. 1
[No State shall ...] make any Thing but gold and silver Coin a Tender in Payment of Debts; ...
Note that there is no such prohibition against Congress, or any delegated power to make anything legal tender. This is primarily because Congress was originally understood to have no power to make anything legal tender outside of federal territories, under Art. I Sec. 8 Cl. 17 and Art. IV Sec. 3 Cl. 2, but in 1868 a Supreme Court packed by Pres. Ulysses S. Grant, in the Legal Tender Cases, allowed Congress to make paper currency issued by the U.S. Treasury, backed by gold, legal tender on state territory, a precedent that remains controversial to this day, when courts allow paper currency not backed by anything to be considered "legal tender".
For all the details of Grant's court packing scheme and their unconstitutional ruling see here - this is a MUST READ.
"The founding fathers were concerned about the unrestrained control of the money supply. One thing they all agreed upon was the limitation on the issuance of money,
Thomas Jefferson warned of the damage that would be caused if the people assigned control of the money supply to the banking sector, "I believe that banking institutions are more dangerous to our liberties than standing armies. Already they have raised up a money aristocracy that has set the government at defiance. This issuing power should be taken from the banks and restored to the people to whom it properly belongs. If the American people ever allow private banks to control the issue of currency, first by inflation, then by deflation, the banks and corporations that will grow up around them will deprive the people of all property until their children will wake up homeless on the continent their fathers conquered. I hope we shall crush in its birth the aristocracy of the moneyed corporations which already dare to challenge our Government to a trial of strength and bid defiance to the laws of our country" Thomas Jefferson, 1791
Many of the founding fathers experienced the damage caused by fiat currency. Most of the revolutionary war was financed by worthless currency called "Continentals".
# The Continental Currency ("Not worth a Continental") that American colonists issued for the Continental Congress to finance the Revolutionary War was replaced by the US Dollar in 1785 when The Continental Congress adopted the dollar as the unit for national currency. At that time, private bank-note companies printed a variety of notes. After adoption of the Constitution in 1789, Congress chartered the First Bank of the United States and authorized it to issue paper bank notes to eliminate confusion and simplify trade. The U.S. Constitution (Section 10) forbids any state from making anything but gold or silver a legal tender. The Federal Monetary System was established in 1792 with the creation of the U.S. Mint in Philadelphia. The first American coins were struck in 1793. The U.S. Coinage Act of 1792, consistent with the Constitution, provided for a U.S. Mint, which stamped silver and gold coins. The importance of this Act cannot be stressed enough. One dollar was defined by statute as a specific weight of gold.
# The Act also invoked the death penalty for anyone found to be debasing money.
# President George Washington mentions the importance of the national currency backed by gold and silver throughout his initial term of office and he contributed his own silver for the initial coins minted.
# The purchase of The US Mint in Philadelphia, was the first money appropriated by Congress for a building to be used for a public purpose. It was purchased for a total of $4,266.67 on July 18, 1792.
Here's the Coinage Act so everyone can read the truth for themselves:
"SEC. 19. And be it further enacted, That if any of the gold or silver coins which shall be struck or coined at the said mint shall be debased or made worse as to the proportion of fine gold or fine silver therein contained, or shall be of less weight or value than the same ought to be pursuant to the directions of this act, through the default or with the connivance of any of the officers or persons who shall be employed at the said mint, for the purpose of profit or gain, or otherwise with a fraudulent intent, and if any of the said officers or persons shall embezzle any of the metals which shall at any time be committed to their charge for the purpose of being coined, or any of the coins which shall be struck or coined at the said mint, every such officer or person who shall commit any or either of the said offences, shall be deemed guilty of felony, and shall suffer death."