If it's possible just try and gently wash it off. Otherwise I would leave it on. If you try and get it off you will probably scratch the coin and decrease its value.
Iron, lead, zinc, gold.
It is impossible to say what a copy coin is worth. Copy coins have no collector value, their only value comes from what the coin is made with. Some high end copies are made out of the same material that the authentic coin is made out of, in this case, it would be gold. Others might be gold plated silver, still others may be gold plated copper, or you might have gold plated steel or lead. Without seeing the coin in person it is impossible to say because there are so many types of copy coins.
To remove lead from a mechanical pencil tip, gently push the lead back into the pencil using the eraser or a small tool. Be careful not to break the lead while doing this.
If it's a miniature coin it's a privately-issued piece and not one of the "American Eagle" coins struck by the US Mint. Its value would depend on its gold content. If the content and fineness are on the back of the coin, multiply the weight by the fineness and multiply that result by the current price of gold (see, e.g., a site like kitco.com). That will give you its retail value; assume about half that amount for what a metal dealer will pay. If the content and fineness are NOT on the back of the coin, it's probably just plated and doesn't have enough gold to be worth very much.
Since copy coins don't have any standards, anyone can make a copy coin out of any material (lead, zinc, gold, silver, copper, etc.) only a coin dealer or jeweler who sees your coin in person can guess at what it is made out of. It has no collector value, the only value comes from the metals used to make it. Most are just gold-plated copper and have no value though.
There is no process to make gold out of lead.
Lead is heavier than gold. Gold has a density of 19.3 g/cm3, while lead has a density of 11.3 g/cm3.
Sell it, buy gold for the money. Technically is impossible to obtain gold from lead.
Biting a coin is not a reliable test for pure gold. Pure gold is a soft metal and would show bite marks easily since it is malleable. However, other metals like lead, which is also soft, can also leave bite marks and can be mistaken for gold. Professional testing methods like acid testing or electronic testing are more accurate for determining the purity of gold.
Get the gold coin from the fountain to pay your admission. The immediate item is a library slip that will lead you to the castle library. (It is on the right side of the room.)
Lead is a dullish grey colour whereas gold - is well - gold in colour. Unless it's white gold, but still it looks nothing like lead.
lead has more protons less densely arranged