with the coins in hand, is there any way of testing for authenticity ? I'm speaking about victorian and edward nickels, dimes, quarters and 50 cent pieces. for example, will the coins not be magnetic whereas fakes will be?
or how accurate is it to weigh the coin and compare it with the stated value from the mint?
There is no one, single test you can do that proves a coin is fake. We don't yet have "Star Trek" tricorders that you can wave at a suspicious coin and it will use magical-science to tell you straight away whether it's fake or not. Whichever test you might try to choose, there will be some fake coins that fail the test, and some that pass.
Magnetism is a property of the metal the coin is made of, not a property of the coin itself. Testing its magnetic properties will tell you if the coin in question is actually made of silver (or some alloy that reacts identically to a magnet as silver does). The cheap, common types of fakes, and most circulating counterfeits, are not made of silver. High-quality fakes designed to fool collectors are probably going to be made of silver - they're probably even going to be made from melted-down old worn-out coins, so the alloy will be an exact match. And if the alloy matches, the magnetic properties will match.
And just a word on silver and magnets. The property we call "magnetism - the capacity to "stick to" a magnet - is more properly called "paramagnetism". Only a few metals (iron, cobalt, nickel, and certain alloys) are paramagnetic. Very few fake silver coins are actually made of iron, steel or some other paramagnetic alloy, so testing whether they stick to a magnet or not isn't usually all that helpful, as most fakes act just like a genuine silver coin and won't stick to a magnet.
All other metals are what we call "diamagnetic". A diamagnetic substance is slightly repelled by a magnetic field, instead of strongly attracted to it. Diamagnetic levitation isn't of much practical use in coin testing, since the effect is so small, but there is another effect we see with silver and magnets: eddy current magnetism. This is where a powerful magnetic field that is moving
generates an opposing magnetic field within a piece of diamagnetic metal that it passes next to. The faster the motion, the stronger the eddy current field that is generated. Silver, being one of the best electrical conductors, generates very powerful eddy current fields.
The net result of this is, that if you take a very powerful magnet - one of those fancy rare-earth magnets that you aren't supposed to let kids play with - and sweep it across a bunch of silver coins sitting on a table, the coins will not
just sit there and do nothing. They will dance around on the table, following the magnet as it moves - they will seem
to be attracted to the magnet, just a little bit, but only while the magnet is moving, and the faster you move the magnet around, the more obvious the effect becomes. Copper and any other metallic alloy will do this also, but to nowhere near the same degree.
There are magnetic "silver coin testers" out there that use eddy current generation as a test for silver. You have to learn how to "read" them (that takes practice, watching how the device reacts to numerous genuine silver and non-silver coins), and they're typically a bit cumbersome to set up out in the marketplace or at a coin show, but they can reliably discern between something silver, and something not-silver.
So now, let's move on to "weight". The weight of an object depends on its size, and the density of the substance it is made from. So, "size" is a property of the coin itself, whereas "density" is a property of the metal is is made from. A fake coin that is the exact same size as a genuine coin, but is made from something other than silver, is likely to have a density that is different from silver, and therefore will weigh less (or sometimes more) than a genuine coin. A fake coin the correct size and made of silver is likely to have the correct weight. And, of course, if they use non-silver alloys but alter the dimensions of the coin with the goal of attaining the correct weight (by, for example, making the fake coin slightly thicker) then the weight test can be fooled. The Chinese fake-makers are actually pretty good at doing this. So again, the weight test will detect some fake coins, but not all of them.
Weight is a much more useful test for fake gold coins, rather than silver, because gold is unusually dense - very few metals have the same high density as gold and most of those substitute-metals are even more expensive and hard-to-get than gold (metals such as platinum and osmium), so fake non-gold coins almost always weigh much, much less than genuine gold. And "making it thicker" to bring the weight up doesn't really work, because gold is over twice as dense as most other metals, so the coin would need to be more than twice the thickness of a genuine coin - the coin would become too suspiciously thick. Tungsten is one of the few easily-obtainable substances that matches gold for density, and while raw tungsten might be cheap, actually working with tungsten is neither cheap nor simple, so only the most sophisticated counterfeiting rackets try to use it, and more usually for fake ingots rather than coins.
Finally, of course, the "weight" of a genuine coin is also affected by its history. A worn coin weighs less than a brand new coin; the more wear it has, the lighter the weight. Corrosion and damage can also change a coin's weight. So, as you can see, trying to use weight, and weight alone, is not a perfect test for fakeness: it will "pass" certain fake coins, and "fail" certain genuine coins. Again, this is where "experience" helps: how much weight loss is expectable for a given degree of wear? That's something you can only find out by weighing hundreds of known-genuine coins all at various stages of wear.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis