A sort of broad question, but I'm generally referring to the time before paper money. Coins were minted, from copper, silver, and gold. Could two coins, minted in difference places, but largely the same (weight, made of gold, etc) be valued differently against each other? Did any type of coin ever suffer from inflation? For example, the florin was ubiquitous for sometime--were other similar gold coins not seen as valuable compared to it, even if they were largely similar?
Certainly metal currency can inflate and deflate as new sources of ore are discovered. According to the 18th century Scottish economist Adam Smith:
The discovery of the abundant mines of America, reduced, in the sixteenth century, the value of gold and silver in Europe to about a third of what it had been before. As it cost less labour to bring those metals from the mine to the market, so, when they were brought thither, they could purchase or command less labour; and this revolution in their value, though perhaps the greatest, is by no means the only one of which history gives some account.
I think the term you're looking for is debased currency rather than inflation. I don't have the knowledge to talk intelligently on the topic, but I hope clarifying the term can help.
A metallic coin can always be melted down and reminted as a different coin with the same metallic content, so the rate of exchange between these coins will rarely exceed the cost of reminting. This is, I think, the question you were asking, but there are several wrinkles.
I assume that by "same weight" you mean the same weight in our modern sense. But in the early modern period weights and measures differed from region to region. So two coins could each be "a pound of silver" and yet one could be heavier, or be of a higher purity than the other, because the pound was different at the mints where each coin was cast.
It was common practice to "clip" coins, i.e. shave metal off the sides. So the longer a coin had been in circulation, the lower the metallic content.
As I mentioned, the weight and purity of a coin, as well as the metal used, was at the discretion of the minting authority. Simply by changing these standards, the same amount of metal could be stretched to mint a larger quantity of coins.
Baylis has already given you the traditional explanation for the inflation of gold and silver currencies; when gold and silver are mined faster than they are sunk into jewelry, vaults, and so on, the price of the metal falls. If you measure all other prices relative to gold (as in the gold standard) or gold and silver (bimetallism), then a higher supply of gold translates into higher prices for all commodities.
But in the last fifty years historians have realized that the supply of gold and silver is inadequate to explain inflation in metallic currencies. The key to understanding this is that most businesses operate on credit, so a promise of a pound of silver is worth nearly as much as a pound of silver itself. Whenever there is an increase in population and commerce, the effective money supply expands as the number of potential commercial transactions that can be the basis for an extension of credit expands.
In the Renaissance it was possible to debase the currency when the ruler needed money, typically adding more copper to the silver or gold alloy. The silver coins of Mary I's reign, for example, had a pretty high copper content to fund her husband Phillip II's wars. The result was a kind of forced loan from the population. It also forced earlier coinage underground- people would hoard the old coins, because they were worth more. Spain's importing gold and silver from its New World colonies also created an inflation, as the money supply increased ( they had to use slaves to dig it out of the ground, in the US now the Federal Reserve can just print more).
Coins were also shaved by people, which is why money changers had small scales to check their weight. Isaac Newton was ( I am pretty sure) the one who introduced a toothed rim to coins, so it would be impossible to shave them without it being obvious.
The biggest impact on the value of gold or silver coins would be the availability of those metals. There is one example I know of in which the value of gold currency collapsed due to someone's actions.
In 1324, the Emperor of Mali, Mansa Musa, went on pilgrimage to Mecca. He traveled across the Sahara with a massive entourage of over 60,000 men. This included 12,000 slaves, each of whom carried a four lbs. golden staff. He had 80 camels that carried between 4,000 and 24,000 lbs. of gold dust. Wherever he went, he spent lavishly and gave gold to the poor.
It is said that when he left Cairo, he had injected so much gold into the city that the value of gold plummeted and stayed depreciated for several years.
See A.J.H. Goodwin's "The Medieval Empire of Ghana," South African Archaeological Bulletin (1957), 108-112 for a quick summation of Mansa Musa's pilgrimage.